IABSD.fr/src/bin/ksh/ksh.1

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• Author : jmc
  Date : 2019-11-26 22:49:01
  Hash : c6b77f58
  Message : some corrections to CDPATH; from chohag

• bin/ksh/ksh.1

• .\"	$OpenBSD: ksh.1,v 1.208 2019/11/26 22:49:01 jmc Exp $
  .\"
  .\"	Public Domain
  .\"
  .Dd $Mdocdate: November 26 2019 $
  .Dt KSH 1
  .Os
  .Sh NAME
  .Nm ksh ,
  .Nm rksh
  .Nd public domain Korn shell
  .Sh SYNOPSIS
  .Nm ksh
  .Bk -words
  .Op Fl +abCefhiklmnpruvXx
  .Op Fl +o Ar option
  .Op Fl c Ar string | Fl s | Ar file Op Ar argument ...
  .Ek
  .Sh DESCRIPTION
  .Nm
  is a command interpreter intended for both interactive and shell
  script use.
  Its command language is a superset of the
  .Xr sh 1
  shell language.
  .Pp
  The options are as follows:
  .Bl -tag -width Ds
  .It Fl c Ar string
  .Nm
  will execute the command(s) contained in
  .Ar string .
  .It Fl i
  Interactive shell.
  A shell is
  .Dq interactive
  if this
  option is used or if both standard input and standard error are attached
  to a
  .Xr tty 4 .
  An interactive shell has job control enabled, ignores the
  .Dv SIGINT ,
  .Dv SIGQUIT ,
  and
  .Dv SIGTERM
  signals, and prints prompts before reading input (see the
  .Ev PS1
  and
  .Ev PS2
  parameters).
  For non-interactive shells, the
  .Ic trackall
  option is on by default (see the
  .Ic set
  command below).
  .It Fl l
  Login shell.
  If the basename the shell is called with (i.e. argv[0])
  starts with
  .Ql -
  or if this option is used,
  the shell is assumed to be a login shell and the shell reads and executes
  the contents of
  .Pa /etc/profile
  and
  .Pa $HOME/.profile
  if they exist and are readable.
  .It Fl p
  Privileged shell.
  A shell is
  .Dq privileged
  if this option is used
  or if the real user ID or group ID does not match the
  effective user ID or group ID (see
  .Xr getuid 2
  and
  .Xr getgid 2 ) .
  A privileged shell does not process
  .Pa $HOME/.profile
  nor the
  .Ev ENV
  parameter (see below).
  Instead, the file
  .Pa /etc/suid_profile
  is processed.
  Clearing the privileged option causes the shell to set
  its effective user ID (group ID) to its real user ID (group ID).
  .It Fl r
  Restricted shell.
  A shell is
  .Dq restricted
  if this
  option is used;
  if the basename the shell was invoked with was
  .Dq rksh ;
  or if the
  .Ev SHELL
  parameter is set to
  .Dq rksh .
  The following restrictions come into effect after the shell processes any
  profile and
  .Ev ENV
  files:
  .Pp
  .Bl -bullet -compact
  .It
  The
  .Ic cd
  command is disabled.
  .It
  The
  .Ev SHELL ,
  .Ev ENV ,
  and
  .Ev PATH
  parameters cannot be changed.
  .It
  Command names can't be specified with absolute or relative paths.
  .It
  The
  .Fl p
  option of the built-in command
  .Ic command
  can't be used.
  .It
  Redirections that create files can't be used (i.e.\&
  .Sq Cm > ,
  .Sq Cm >| ,
  .Sq Cm >> ,
  .Sq Cm <> ) .
  .El
  .It Fl s
  The shell reads commands from standard input; all non-option arguments
  are positional parameters.
  .El
  .Pp
  In addition to the above, the options described in the
  .Ic set
  built-in command can also be used on the command line:
  both
  .Op Fl +abCefhkmnuvXx
  and
  .Op Fl +o Ar option
  can be used for single letter or long options, respectively.
  .Pp
  If neither the
  .Fl c
  nor the
  .Fl s
  option is specified, the first non-option argument specifies the name
  of a file the shell reads commands from.
  If there are no non-option
  arguments, the shell reads commands from the standard input.
  The name of the shell (i.e. the contents of $0)
  is determined as follows: if the
  .Fl c
  option is used and there is a non-option argument, it is used as the name;
  if commands are being read from a file, the file is used as the name;
  otherwise, the basename the shell was called with (i.e. argv[0]) is used.
  .Pp
  If the
  .Ev ENV
  parameter is set when an interactive shell starts (or,
  in the case of login shells,
  after any profiles are processed), its value is subjected to parameter,
  command, arithmetic, and tilde
  .Pq Sq ~
  substitution and the resulting file
  (if any) is read and executed.
  In order to have an interactive (as opposed to login) shell
  process a startup file,
  .Ev ENV
  may be set and exported (see below) in
  .Pa $HOME/.profile
  \- future interactive shell invocations will process any file pointed to by
  .Ev $ENV :
  .Pp
  .Dl export ENV=$HOME/.kshrc
  .Pp
  .Pa $HOME/.kshrc
  is then free to specify instructions for interactive shells.
  For example, the global configuration file may be sourced:
  .Bd -literal -offset indent
  \&. /etc/ksh.kshrc
  .Ed
  .Pp
  The above strategy may be employed to keep
  setup procedures for login shells in
  .Pa $HOME/.profile
  and setup procedures for interactive shells in
  .Pa $HOME/.kshrc .
  Of course, since login shells are also interactive,
  any commands placed in
  .Pa $HOME/.kshrc
  will be executed by login shells too.
  .Pp
  The exit status of the shell is 127 if the command file specified on the
  command line could not be opened, or non-zero if a fatal syntax error
  occurred during the execution of a script.
  In the absence of fatal errors,
  the exit status is that of the last command executed, or zero, if no
  command is executed.
  .Ss Command syntax
  The shell begins parsing its input by breaking it into
  .Em words .
  Words, which are sequences of characters, are delimited by unquoted whitespace
  characters (space, tab, and newline) or meta-characters
  .Po
  .Ql < ,
  .Ql > ,
  .Ql | ,
  .Ql \&; ,
  .Ql \&( ,
  .Ql \&) ,
  and
  .Ql &
  .Pc .
  Aside from delimiting words, spaces and tabs are ignored, while newlines
  usually delimit commands.
  The meta-characters are used in building the following
  .Em tokens :
  .Sq Cm < ,
  .Sq Cm <& ,
  .Sq Cm << ,
  .Sq Cm > ,
  .Sq Cm >& ,
  .Sq Cm >> ,
  etc. are used to specify redirections (see
  .Sx Input/output redirection
  below);
  .Ql |
  is used to create pipelines;
  .Ql |&
  is used to create co-processes (see
  .Sx Co-processes
  below);
  .Ql \&;
  is used to separate commands;
  .Ql &
  is used to create asynchronous pipelines;
  .Ql &&
  and
  .Ql ||
  are used to specify conditional execution;
  .Ql ;;
  is used in
  .Ic case
  statements;
  .Ql (( .. ))
  is used in arithmetic expressions;
  and lastly,
  .Ql \&( .. )\&
  is used to create subshells.
  .Pp
  Whitespace and meta-characters can be quoted individually using a backslash
  .Pq Sq \e ,
  or in groups using double
  .Pq Sq \&"
  or single
  .Pq Sq '
  quotes.
  The following characters are also treated specially by the
  shell and must be quoted if they are to represent themselves:
  .Ql \e ,
  .Ql \&" ,
  .Ql ' ,
  .Ql # ,
  .Ql $ ,
  .Ql ` ,
  .Ql ~ ,
  .Ql { ,
  .Ql } ,
  .Ql * ,
  .Ql \&? ,
  and
  .Ql \&[ .
  The first three of these are the above mentioned quoting characters (see
  .Sx Quoting
  below);
  .Ql # ,
  if used at the beginning of a word, introduces a comment \(em everything after
  the
  .Ql #
  up to the nearest newline is ignored;
  .Ql $
  is used to introduce parameter, command, and arithmetic substitutions (see
  .Sx Substitution
  below);
  .Ql `
  introduces an old-style command substitution (see
  .Sx Substitution
  below);
  .Ql ~
  begins a directory expansion (see
  .Sx Tilde expansion
  below);
  .Ql {
  and
  .Ql }
  delimit
  .Xr csh 1 Ns -style
  alternations (see
  .Sx Brace expansion
  below);
  and finally,
  .Ql * ,
  .Ql \&? ,
  and
  .Ql \&[
  are used in file name generation (see
  .Sx File name patterns
  below).
  .Pp
  As words and tokens are parsed, the shell builds commands, of which there
  are two basic types:
  .Em simple-commands ,
  typically programs that are executed, and
  .Em compound-commands ,
  such as
  .Ic for
  and
  .Ic if
  statements, grouping constructs, and function definitions.
  .Pp
  A simple-command consists of some combination of parameter assignments
  (see
  .Sx Parameters
  below),
  input/output redirections (see
  .Sx Input/output redirections
  below),
  and command words; the only restriction is that parameter assignments come
  before any command words.
  The command words, if any, define the command
  that is to be executed and its arguments.
  The command may be a shell built-in command, a function,
  or an external command
  (i.e. a separate executable file that is located using the
  .Ev PATH
  parameter; see
  .Sx Command execution
  below).
  .Pp
  All command constructs have an exit status.
  For external commands,
  this is related to the status returned by
  .Xr wait 2
  (if the command could not be found, the exit status is 127; if it could not
  be executed, the exit status is 126).
  The exit status of other command
  constructs (built-in commands, functions, compound-commands, pipelines, lists,
  etc.) are all well-defined and are described where the construct is
  described.
  The exit status of a command consisting only of parameter
  assignments is that of the last command substitution performed during the
  parameter assignment or 0 if there were no command substitutions.
  .Pp
  Commands can be chained together using the
  .Ql |
  token to form pipelines, in which the standard output of each command but the
  last is piped (see
  .Xr pipe 2 )
  to the standard input of the following command.
  The exit status of a pipeline is that of its last command.
  A pipeline may be prefixed by the
  .Ql \&!
  reserved word, which causes the exit status of the pipeline to be logically
  complemented: if the original status was 0, the complemented status will be 1;
  if the original status was not 0, the complemented status will be 0.
  .Pp
  .Em Lists
  of commands can be created by separating pipelines by any of the following
  tokens:
  .Ql && ,
  .Ql || ,
  .Ql & ,
  .Ql |& ,
  and
  .Ql \&; .
  The first two are for conditional execution:
  .Dq Ar cmd1 No && Ar cmd2
  executes
  .Ar cmd2
  only if the exit status of
  .Ar cmd1
  is zero;
  .Ql ||
  is the opposite \(em
  .Ar cmd2
  is executed only if the exit status of
  .Ar cmd1
  is non-zero.
  .Ql &&
  and
  .Ql ||
  have equal precedence which is higher than that of
  .Ql & ,
  .Ql |& ,
  and
  .Ql \&; ,
  which also have equal precedence.
  The
  .Ql &&
  and
  .Ql ||
  operators are
  .Qq left-associative .
  For example, both of these commands will print only
  .Qq bar :
  .Bd -literal -offset indent
  $ false && echo foo || echo bar
  $ true || echo foo && echo bar
  .Ed
  .Pp
  The
  .Ql &
  token causes the preceding command to be executed asynchronously; that is,
  the shell starts the command but does not wait for it to complete (the shell
  does keep track of the status of asynchronous commands; see
  .Sx Job control
  below).
  When an asynchronous command is started when job control is disabled
  (i.e. in most scripts), the command is started with signals
  .Dv SIGINT
  and
  .Dv SIGQUIT
  ignored and with input redirected from
  .Pa /dev/null
  (however, redirections specified in the asynchronous command have precedence).
  The
  .Ql |&
  operator starts a co-process which is a special kind of asynchronous process
  (see
  .Sx Co-processes
  below).
  A command must follow the
  .Ql &&
  and
  .Ql ||
  operators, while it need not follow
  .Ql & ,
  .Ql |& ,
  or
  .Ql \&; .
  The exit status of a list is that of the last command executed, with the
  exception of asynchronous lists, for which the exit status is 0.
  .Pp
  Compound commands are created using the following reserved words.
  These words
  are only recognized if they are unquoted and if they are used as the first
  word of a command (i.e. they can't be preceded by parameter assignments or
  redirections):
  .Bd -literal -offset indent
  case   esac       in       until   ((   }
  do     fi         name     while   ))
  done   for        select   !       [[
  elif   function   then     (       ]]
  else   if         time     )       {
  .Ed
  .Pp
  .Sy Note :
  Some shells (but not this one) execute control structure commands in a
  subshell when one or more of their file descriptors are redirected, so any
  environment changes inside them may fail.
  To be portable, the
  .Ic exec
  statement should be used instead to redirect file descriptors before the
  control structure.
  .Pp
  In the following compound command descriptions, command lists (denoted as
  .Em list )
  that are followed by reserved words must end with a semicolon, a newline, or
  a (syntactically correct) reserved word.
  For example, the following are all valid:
  .Bd -literal -offset indent
  $ { echo foo; echo bar; }
  $ { echo foo; echo bar<newline> }
  $ { { echo foo; echo bar; } }
  .Ed
  .Pp
  This is not valid:
  .Pp
  .Dl $ { echo foo; echo bar }
  .Bl -tag -width Ds
  .It Pq Ar list
  Execute
  .Ar list
  in a subshell.
  There is no implicit way to pass environment changes from a
  subshell back to its parent.
  .It { Ar list ; No }
  Compound construct;
  .Ar list
  is executed, but not in a subshell.
  Note that
  .Ql {
  and
  .Ql }
  are reserved words, not meta-characters.
  .It Xo Ic case Ar word Cm in
  .Oo Op \&(
  .Ar pattern
  .Op | Ar pattern
  .No ... )
  .Ar list No ;;\ \& Oc ... Cm esac
  .Xc
  The
  .Ic case
  statement attempts to match
  .Ar word
  against a specified
  .Ar pattern ;
  the
  .Ar list
  associated with the first successfully matched pattern is executed.
  Patterns used in
  .Ic case
  statements are the same as those used for file name patterns except that the
  restrictions regarding
  .Ql \&.
  and
  .Ql /
  are dropped.
  Note that any unquoted space before and after a pattern is
  stripped; any space within a pattern must be quoted.
  Both the word and the
  patterns are subject to parameter, command, and arithmetic substitution, as
  well as tilde substitution.
  For historical reasons, open and close braces may be used instead of
  .Cm in
  and
  .Cm esac
  e.g.\&
  .Ic case $foo { *) echo bar; } .
  The exit status of a
  .Ic case
  statement is that of the executed
  .Ar list ;
  if no
  .Ar list
  is executed, the exit status is zero.
  .It Xo Ic for Ar name
  .Op Cm in Op Ar word ... ;
  .Cm do Ar list ; Cm done
  .Xc
  For each
  .Ar word
  in the specified word list, the parameter
  .Ar name
  is set to the word and
  .Ar list
  is executed.
  If
  .Cm in
  is not used to specify a word list, the positional parameters
  ($1, $2, etc.)\&
  are used instead.
  For historical reasons, open and close braces may be used instead of
  .Cm do
  and
  .Cm done
  e.g.\&
  .Ic for i; { echo $i; } .
  The exit status of a
  .Ic for
  statement is the last exit status of
  .Ar list .
  If there are no items,
  .Ar list
  is not executed and the exit status is zero.
  .It Xo Ic if Ar list ;
  .Cm then Ar list ;
  .Oo Cm elif Ar list ;
  .Cm then Ar list ; Oc ...
  .Oo Cm else Ar list ; Oc
  .Cm fi
  .Xc
  If the exit status of the first
  .Ar list
  is zero, the second
  .Ar list
  is executed; otherwise, the
  .Ar list
  following the
  .Cm elif ,
  if any, is executed with similar consequences.
  If all the lists following the
  .Ic if
  and
  .Cm elif Ns s
  fail (i.e. exit with non-zero status), the
  .Ar list
  following the
  .Cm else
  is executed.
  The exit status of an
  .Ic if
  statement is that of non-conditional
  .Ar list
  that is executed; if no non-conditional
  .Ar list
  is executed, the exit status is zero.
  .It Xo Ic select Ar name
  .Oo Cm in Ar word No ... Oc ;
  .Cm do Ar list ; Cm done
  .Xc
  The
  .Ic select
  statement provides an automatic method of presenting the user with a menu and
  selecting from it.
  An enumerated list of the specified
  .Ar word Ns (s)
  is printed on standard error, followed by a prompt
  .Po
  .Ev PS3 :
  normally
  .Sq #?\ \&
  .Pc .
  A number corresponding to one of the enumerated words is then read from
  standard input,
  .Ar name
  is set to the selected word (or unset if the selection is not valid),
  .Ev REPLY
  is set to what was read (leading/trailing space is stripped), and
  .Ar list
  is executed.
  If a blank line (i.e. zero or more
  .Ev IFS
  characters) is entered, the menu is reprinted without executing
  .Ar list .
  .Pp
  When
  .Ar list
  completes, the enumerated list is printed if
  .Ev REPLY
  is
  .Dv NULL ,
  the prompt is printed, and so on.
  This process continues until an end-of-file
  is read, an interrupt is received, or a
  .Ic break
  statement is executed inside the loop.
  If
  .Dq in word ...
  is omitted, the positional parameters are used
  (i.e. $1, $2, etc.).
  For historical reasons, open and close braces may be used instead of
  .Cm do
  and
  .Cm done
  e.g.\&
  .Ic select i; { echo $i; } .
  The exit status of a
  .Ic select
  statement is zero if a
  .Ic break
  statement is used to exit the loop, non-zero otherwise.
  .It Xo Ic until Ar list ;
  .Cm do Ar list ;
  .Cm done
  .Xc
  This works like
  .Ic while ,
  except that the body is executed only while the exit status of the first
  .Ar list
  is non-zero.
  .It Xo Ic while Ar list ;
  .Cm do Ar list ;
  .Cm done
  .Xc
  A
  .Ic while
  is a pre-checked loop.
  Its body is executed as often as the exit status of the first
  .Ar list
  is zero.
  The exit status of a
  .Ic while
  statement is the last exit status of the
  .Ar list
  in the body of the loop; if the body is not executed, the exit status is zero.
  .It Xo Ic function Ar name
  .No { Ar list ; No }
  .Xc
  Defines the function
  .Ar name
  (see
  .Sx Functions
  below).
  Note that redirections specified after a function definition are
  performed whenever the function is executed, not when the function definition
  is executed.
  .It Ar name Ns () Ar command
  Mostly the same as
  .Ic function
  (see
  .Sx Functions
  below).
  .It Xo Ic time Op Fl p
  .Op Ar pipeline
  .Xc
  The
  .Ic time
  reserved word is described in the
  .Sx Command execution
  section.
  .It Ic (( Ar expression Cm ))
  The arithmetic expression
  .Ar expression
  is evaluated; equivalent to
  .Ic let Ar expression
  (see
  .Sx Arithmetic expressions
  and the
  .Ic let
  command, below).
  .It Ic [[ Ar expression Cm ]]
  Similar to the
  .Ic test
  and
  .Ic \&[ No ... Cm \&]
  commands (described later), with the following exceptions:
  .Bl -bullet -offset indent
  .It
  Field splitting and file name generation are not performed on arguments.
  .It
  The
  .Fl a
  .Pq AND
  and
  .Fl o
  .Pq OR
  operators are replaced with
  .Ql &&
  and
  .Ql || ,
  respectively.
  .It
  Operators (e.g.\&
  .Sq Fl f ,
  .Sq = ,
  .Sq \&! )
  must be unquoted.
  .It
  The second operand of the
  .Sq !=
  and
  .Sq =
  expressions are patterns (e.g. the comparison
  .Ic [[ foobar = f*r ]]
  succeeds).
  .It
  The
  .Ql <
  and
  .Ql >
  binary operators do not need to be quoted with the
  .Ql \e
  character.
  .It
  The single argument form of
  .Ic test ,
  which tests if the argument has a non-zero length, is not valid; explicit
  operators must always be used e.g. instead of
  .No \&[ Ar str No \&]
  use
  .No \&[[ -n Ar str No \&]] .
  .It
  Parameter, command, and arithmetic substitutions are performed as expressions
  are evaluated and lazy expression evaluation is used for the
  .Ql &&
  and
  .Ql ||
  operators.
  This means that in the following statement,
  .Ic $(< foo)
  is evaluated if and only if the file
  .Pa foo
  exists and is readable:
  .Bd -literal -offset indent
  $ [[ -r foo && $(< foo) = b*r ]]
  .Ed
  .El
  .El
  .Ss Quoting
  Quoting is used to prevent the shell from treating characters or words
  specially.
  There are three methods of quoting.
  First,
  .Ql \e
  quotes the following character, unless it is at the end of a line, in which
  case both the
  .Ql \e
  and the newline are stripped.
  Second, a single quote
  .Pq Sq '
  quotes everything up to the next single quote (this may span lines).
  Third, a double quote
  .Pq Sq \&"
  quotes all characters, except
  .Ql $ ,
  .Ql `
  and
  .Ql \e ,
  up to the next unquoted double quote.
  .Ql $
  and
  .Ql `
  inside double quotes have their usual meaning (i.e. parameter, command, or
  arithmetic substitution) except no field splitting is carried out on the
  results of double-quoted substitutions.
  If a
  .Ql \e
  inside a double-quoted string is followed by
  .Ql \e ,
  .Ql $ ,
  .Ql ` ,
  or
  .Ql \&" ,
  it is replaced by the second character; if it is followed by a newline, both
  the
  .Ql \e
  and the newline are stripped; otherwise, both the
  .Ql \e
  and the character following are unchanged.
  .Ss Aliases
  There are two types of aliases: normal command aliases and tracked aliases.
  Command aliases are normally used as a short hand for a long or often used
  command.
  The shell expands command aliases (i.e. substitutes the alias name
  for its value) when it reads the first word of a command.
  An expanded alias is re-processed to check for more aliases.
  If a command alias ends in a
  space or tab, the following word is also checked for alias expansion.
  The alias expansion process stops when a word that is not an alias is found,
  when a quoted word is found, or when an alias word that is currently being
  expanded is found.
  .Pp
  The following command aliases are defined automatically by the shell:
  .Pp
  .Bl -item -compact -offset indent
  .It
  .Ic autoload Ns ='typeset -fu'
  .It
  .Ic functions Ns ='typeset -f'
  .It
  .Ic hash Ns ='alias -t'
  .It
  .Ic history Ns ='fc -l'
  .It
  .Ic integer Ns ='typeset -i'
  .It
  .Ic local Ns ='typeset'
  .It
  .Ic login Ns ='exec login'
  .It
  .Ic nohup Ns ='nohup '
  .It
  .Ic r Ns ='fc -s'
  .It
  .Ic stop Ns ='kill -STOP'
  .El
  .Pp
  Tracked aliases allow the shell to remember where it found a particular
  command.
  The first time the shell does a path search for a command that is
  marked as a tracked alias, it saves the full path of the command.
  The next
  time the command is executed, the shell checks the saved path to see that it
  is still valid, and if so, avoids repeating the path search.
  Tracked aliases can be listed and created using
  .Ic alias -t .
  Note that changing the
  .Ev PATH
  parameter clears the saved paths for all tracked aliases.
  If the
  .Ic trackall
  option is set (i.e.\&
  .Ic set -o Ic trackall
  or
  .Ic set -h ) ,
  the shell tracks all commands.
  This option is set automatically for non-interactive shells.
  For interactive shells, only the following commands are
  automatically tracked:
  .Xr cat 1 ,
  .Xr cc 1 ,
  .Xr chmod 1 ,
  .Xr cp 1 ,
  .Xr date 1 ,
  .Xr ed 1 ,
  .Sy emacs ,
  .Xr grep 1 ,
  .Xr ls 1 ,
  .Xr mail 1 ,
  .Xr make 1 ,
  .Xr mv 1 ,
  .Xr pr 1 ,
  .Xr rm 1 ,
  .Xr sed 1 ,
  .Xr sh 1 ,
  .Xr vi 1 ,
  and
  .Xr who 1 .
  .Ss Substitution
  The first step the shell takes in executing a simple-command is to perform
  substitutions on the words of the command.
  There are three kinds of
  substitution: parameter, command, and arithmetic.
  Parameter substitutions,
  which are described in detail in the next section, take the form
  .Pf $ Ar name
  or
  .Pf ${ Ar ... Ns } ;
  command substitutions take the form
  .Pf $( Ar command )
  or
  .Pf ` Ar command Ns ` ;
  and arithmetic substitutions take the form
  .Pf $(( Ar expression ) ) .
  .Pp
  If a substitution appears outside of double quotes, the results of the
  substitution are generally subject to word or field splitting according to
  the current value of the
  .Ev IFS
  parameter.
  The
  .Ev IFS
  parameter specifies a list of characters which are used to break a string up
  into several words; any characters from the set space, tab, and newline that
  appear in the
  .Ev IFS
  characters are called
  .Dq IFS whitespace .
  Sequences of one or more
  .Ev IFS
  whitespace characters, in combination with zero or one
  .Pf non- Ev IFS
  whitespace
  characters, delimit a field.
  As a special case, leading and trailing
  .Ev IFS
  whitespace is stripped (i.e. no leading or trailing empty field is created by
  it); leading
  .Pf non- Ev IFS
  whitespace does create an empty field.
  .Pp
  Example: If
  .Ev IFS
  is set to
  .Dq <space>: ,
  and VAR is set to
  .Dq <space>A<space>:<space><space>B::D ,
  the substitution for $VAR results in four fields:
  .Sq A ,
  .Sq B ,
  .Sq
  (an empty field),
  and
  .Sq D .
  Note that if the
  .Ev IFS
  parameter is set to the
  .Dv NULL
  string, no field splitting is done; if the parameter is unset, the default
  value of space, tab, and newline is used.
  .Pp
  Also, note that the field splitting applies only to the immediate result of
  the substitution.
  Using the previous example, the substitution for $VAR:E
  results in the fields:
  .Sq A ,
  .Sq B ,
  .Sq ,
  and
  .Sq D:E ,
  not
  .Sq A ,
  .Sq B ,
  .Sq ,
  .Sq D ,
  and
  .Sq E .
  This behavior is POSIX compliant, but incompatible with some other shell
  implementations which do field splitting on the word which contained the
  substitution or use
  .Dv IFS
  as a general whitespace delimiter.
  .Pp
  The results of substitution are, unless otherwise specified, also subject to
  brace expansion and file name expansion (see the relevant sections below).
  .Pp
  A command substitution is replaced by the output generated by the specified
  command, which is run in a subshell.
  For
  .Pf $( Ar command )
  substitutions, normal quoting rules are used when
  .Ar command
  is parsed; however, for the
  .Pf ` Ar command Ns `
  form, a
  .Ql \e
  followed by any of
  .Ql $ ,
  .Ql ` ,
  or
  .Ql \e
  is stripped (a
  .Ql \e
  followed by any other character is unchanged).
  As a special case in command substitutions, a command of the form
  .Pf < Ar file
  is interpreted to mean substitute the contents of
  .Ar file .
  Note that
  .Ic $(< foo)
  has the same effect as
  .Ic $(cat foo) ,
  but it is carried out more efficiently because no process is started.
  .Pp
  Arithmetic substitutions are replaced by the value of the specified expression.
  For example, the command
  .Ic echo $((2+3*4))
  prints 14.
  See
  .Sx Arithmetic expressions
  for a description of an expression.
  .Ss Parameters
  Parameters are shell variables; they can be assigned values and their values
  can be accessed using a parameter substitution.
  A parameter name is either one
  of the special single punctuation or digit character parameters described
  below, or a letter followed by zero or more letters or digits
  .Po
  .Ql _
  counts as a letter
  .Pc .
  The latter form can be treated as arrays by appending an array index of the
  form
  .Op Ar expr
  where
  .Ar expr
  is an arithmetic expression.
  Parameter substitutions take the form
  .Pf $ Ar name ,
  .Pf ${ Ar name Ns } ,
  or
  .Sm off
  .Pf ${ Ar name Bo Ar expr Bc }
  .Sm on
  where
  .Ar name
  is a parameter name.
  If
  .Ar expr
  is a literal
  .Ql @
  then the named array is expanded using the same quoting rules as
  .Ql $@ ,
  while if
  .Ar expr
  is a literal
  .Ql *
  then the named array is expanded using the same quoting rules as
  .Ql $* .
  If substitution is performed on a parameter
  (or an array parameter element)
  that is not set, a null string is substituted unless the
  .Ic nounset
  option
  .Po
  .Ic set Fl o Ic nounset
  or
  .Ic set Fl u
  .Pc
  is set, in which case an error occurs.
  .Pp
  Parameters can be assigned values in a number of ways.
  First, the shell implicitly sets some parameters like
  .Ql # ,
  .Ql PWD ,
  and
  .Ql $ ;
  this is the only way the special single character parameters are set.
  Second, parameters are imported from the shell's environment at startup.
  Third, parameters can be assigned values on the command line: for example,
  .Ic FOO=bar
  sets the parameter
  .Dq FOO
  to
  .Dq bar ;
  multiple parameter assignments can be given on a single command line and they
  can be followed by a simple-command, in which case the assignments are in
  effect only for the duration of the command (such assignments are also
  exported; see below for the implications of this).
  Note that both the parameter name and the
  .Ql =
  must be unquoted for the shell to recognize a parameter assignment.
  The fourth way of setting a parameter is with the
  .Ic export ,
  .Ic readonly ,
  and
  .Ic typeset
  commands; see their descriptions in the
  .Sx Command execution
  section.
  Fifth,
  .Ic for
  and
  .Ic select
  loops set parameters as well as the
  .Ic getopts ,
  .Ic read ,
  and
  .Ic set -A
  commands.
  Lastly, parameters can be assigned values using assignment operators
  inside arithmetic expressions (see
  .Sx Arithmetic expressions
  below) or using the
  .Pf ${ Ar name Ns = Ns Ar value Ns }
  form of the parameter substitution (see below).
  .Pp
  Parameters with the export attribute (set using the
  .Ic export
  or
  .Ic typeset Fl x
  commands, or by parameter assignments followed by simple commands) are put in
  the environment (see
  .Xr environ 7 )
  of commands run by the shell as
  .Ar name Ns = Ns Ar value
  pairs.
  The order in which parameters appear in the environment of a command is
  unspecified.
  When the shell starts up, it extracts parameters and their values
  from its environment and automatically sets the export attribute for those
  parameters.
  .Pp
  Modifiers can be applied to the
  .Pf ${ Ar name Ns }
  form of parameter substitution:
  .Bl -tag -width Ds
  .Sm off
  .It ${ Ar name No :- Ar word No }
  .Sm on
  If
  .Ar name
  is set and not
  .Dv NULL ,
  it is substituted; otherwise,
  .Ar word
  is substituted.
  .Sm off
  .It ${ Ar name No :+ Ar word No }
  .Sm on
  If
  .Ar name
  is set and not
  .Dv NULL ,
  .Ar word
  is substituted; otherwise, nothing is substituted.
  .Sm off
  .It ${ Ar name No := Ar word No }
  .Sm on
  If
  .Ar name
  is set and not
  .Dv NULL ,
  it is substituted; otherwise, it is assigned
  .Ar word
  and the resulting value of
  .Ar name
  is substituted.
  .Sm off
  .It ${ Ar name No :? Ar word No }
  .Sm on
  If
  .Ar name
  is set and not
  .Dv NULL ,
  it is substituted; otherwise,
  .Ar word
  is printed on standard error (preceded by
  .Ar name : )
  and an error occurs (normally causing termination of a shell script, function,
  or script sourced using the
  .Sq \&.
  built-in).
  If
  .Ar word
  is omitted, the string
  .Dq parameter null or not set
  is used instead.
  .El
  .Pp
  In the above modifiers, the
  .Ql \&:
  can be omitted, in which case the conditions only depend on
  .Ar name
  being set (as opposed to set and not
  .Dv NULL ) .
  If
  .Ar word
  is needed, parameter, command, arithmetic, and tilde substitution are performed
  on it; if
  .Ar word
  is not needed, it is not evaluated.
  .Pp
  The following forms of parameter substitution can also be used:
  .Pp
  .Bl -tag -width Ds -compact
  .It Pf ${# Ar name Ns }
  The number of positional parameters if
  .Ar name
  is
  .Ql * ,
  .Ql @ ,
  or not specified; otherwise the length of the string value of parameter
  .Ar name .
  .Pp
  .It Pf ${# Ar name Ns [*]}
  .It Pf ${# Ar name Ns [@]}
  The number of elements in the array
  .Ar name .
  .Pp
  .It Pf ${ Ar name Ns # Ns Ar pattern Ns }
  .It Pf ${ Ar name Ns ## Ns Ar pattern Ns }
  If
  .Ar pattern
  matches the beginning of the value of parameter
  .Ar name ,
  the matched text is deleted from the result of substitution.
  A single
  .Ql #
  results in the shortest match, and two
  of them result in the longest match.
  .Pp
  .It Pf ${ Ar name Ns % Ns Ar pattern Ns }
  .It Pf ${ Ar name Ns %% Ns Ar pattern Ns }
  Like ${..#..} substitution, but it deletes from the end of the value.
  .El
  .Pp
  The following special parameters are implicitly set by the shell and cannot be
  set directly using assignments:
  .Bl -tag -width "1 ... 9"
  .It Ev \&!
  Process ID of the last background process started.
  If no background processes have been started, the parameter is not set.
  .It Ev \&#
  The number of positional parameters ($1, $2, etc.).
  .It Ev \&$
  The PID of the shell, or the PID of the original shell if it is a subshell.
  Do
  .Em NOT
  use this mechanism for generating temporary file names; see
  .Xr mktemp 1
  instead.
  .It Ev -
  The concatenation of the current single letter options (see the
  .Ic set
  command below for a list of options).
  .It Ev \&?
  The exit status of the last non-asynchronous command executed.
  If the last command was killed by a signal,
  .Ic $?\&
  is set to 128 plus the signal number.
  .It Ev 0
  The name of the shell, determined as follows:
  the first argument to
  .Nm
  if it was invoked with the
  .Fl c
  option and arguments were given; otherwise the
  .Ar file
  argument, if it was supplied;
  or else the basename the shell was invoked with (i.e.\&
  .Li argv[0] ) .
  .Ev $0
  is also set to the name of the current script or
  the name of the current function, if it was defined with the
  .Ic function
  keyword (i.e. a Korn shell style function).
  .It Ev 1 No ... Ev 9
  The first nine positional parameters that were supplied to the shell, function,
  or script sourced using the
  .Sq \&.
  built-in.
  Further positional parameters may be accessed using
  .Pf ${ Ar number Ns } .
  .It Ev *
  All positional parameters (except parameter 0) i.e. $1, $2, $3, ...
  If used
  outside of double quotes, parameters are separate words (which are subjected
  to word splitting); if used within double quotes, parameters are separated
  by the first character of the
  .Ev IFS
  parameter (or the empty string if
  .Ev IFS
  is
  .Dv NULL ) .
  .It Ev @
  Same as
  .Ic $* ,
  unless it is used inside double quotes, in which case a separate word is
  generated for each positional parameter.
  If there are no positional parameters, no word is generated.
  .Ic $@
  can be used to access arguments, verbatim, without losing
  .Dv NULL
  arguments or splitting arguments with spaces.
  .El
  .Pp
  The following parameters are set and/or used by the shell:
  .Bl -tag -width "EXECSHELL"
  .It Ev _ No (underscore)
  When an external command is executed by the shell, this parameter is set in the
  environment of the new process to the path of the executed command.
  In interactive use, this parameter is also set in the parent shell to the last
  word of the previous command.
  When
  .Ev MAILPATH
  messages are evaluated, this parameter contains the name of the file that
  changed (see the
  .Ev MAILPATH
  parameter, below).
  .It Ev CDPATH
  Search path for the
  .Ic cd
  built-in command.
  It works the same way as
  .Ev PATH
  for those directories not beginning with
  .Ql /
  or
  .Ql .\&
  in
  .Ic cd
  commands.
  Note that if
  .Ev CDPATH
  is set and does not contain
  .Sq \&.
  or an empty path, the current directory is not searched.
  Also, the
  .Ic cd
  built-in command will display the resulting directory when a match is found
  in any search path other than the empty path.
  .It Ev COLUMNS
  Set to the number of columns on the terminal or window.
  Currently set to the
  .Dq cols
  value as reported by
  .Xr stty 1
  if that value is non-zero.
  This parameter is used by the interactive line editing modes, and by the
  .Ic select ,
  .Ic set -o ,
  and
  .Ic kill -l
  commands to format information columns.
  .It Ev EDITOR
  If the
  .Ev VISUAL
  parameter is not set, this parameter controls the command-line editing mode for
  interactive shells.
  See the
  .Ev VISUAL
  parameter below for how this works.
  .Pp
  Note:
  traditionally,
  .Ev EDITOR
  was used to specify the name of an (old-style) line editor, such as
  .Xr ed 1 ,
  and
  .Ev VISUAL
  was used to specify a (new-style) screen editor, such as
  .Xr vi 1 .
  Hence if
  .Ev VISUAL
  is set, it overrides
  .Ev EDITOR .
  .It Ev ENV
  If this parameter is found to be set after any profile files are executed, the
  expanded value is used as a shell startup file.
  It typically contains function and alias definitions.
  .It Ev EXECSHELL
  If set, this parameter is assumed to contain the shell that is to be used to
  execute commands that
  .Xr execve 2
  fails to execute and which do not start with a
  .Dq #! Ns Ar shell
  sequence.
  .It Ev FCEDIT
  The editor used by the
  .Ic fc
  command (see below).
  .It Ev FPATH
  Like
  .Ev PATH ,
  but used when an undefined function is executed to locate the file defining the
  function.
  It is also searched when a command can't be found using
  .Ev PATH .
  See
  .Sx Functions
  below for more information.
  .It Ev HISTCONTROL
  A colon separated list of history settings.
  If
  .Li ignoredups
  is present, lines identical to the previous history line will not be saved.
  If
  .Li ignorespace
  is present, lines starting with a space will not be saved.
  Unknown settings are ignored.
  .It Ev HISTFILE
  The name of the file used to store command history.
  When assigned to, history is loaded from the specified file.
  Also, several invocations of the shell
  running on the same machine will share history if their
  .Ev HISTFILE
  parameters all point to the same file.
  .Pp
  .Sy Note :
  If
  .Ev HISTFILE
  isn't set, no history file is used.
  This is different from the original Korn shell, which uses
  .Pa $HOME/.sh_history .
  .It Ev HISTSIZE
  The number of commands normally stored for history.
  The default is 500.
  .It Ev HOME
  The default directory for the
  .Ic cd
  command and the value substituted for an unqualified
  .Ic ~
  (see
  .Sx Tilde expansion
  below).
  .It Ev IFS
  Internal field separator, used during substitution and by the
  .Ic read
  command, to split values into distinct arguments; normally set to space, tab,
  and newline.
  See
  .Sx Substitution
  above for details.
  .Pp
  .Sy Note :
  This parameter is not imported from the environment when the shell is
  started.
  .It Ev KSH_VERSION
  The version of the shell and the date the version was created (read-only).
  .It Ev LINENO
  The line number of the function or shell script that is currently being
  executed.
  .It Ev LINES
  Set to the number of lines on the terminal or window.
  .It Ev MAIL
  If set, the user will be informed of the arrival of mail in the named file.
  This parameter is ignored if the
  .Ev MAILPATH
  parameter is set.
  .It Ev MAILCHECK
  How often, in seconds, the shell will check for mail in the file(s) specified
  by
  .Ev MAIL
  or
  .Ev MAILPATH .
  If set to 0, the shell checks before each prompt.
  The default is 600 (10 minutes).
  .It Ev MAILPATH
  A list of files to be checked for mail.
  The list is colon separated, and each file may be followed by a
  .Ql \&?
  and a message to be printed if new mail has arrived.
  Command, parameter, and
  arithmetic substitution is performed on the message and, during substitution,
  the parameter
  .Ic $_
  contains the name of the file.
  The default message is
  .Dq you have mail in $_ .
  .It Ev OLDPWD
  The previous working directory.
  Unset if
  .Ic cd
  has not successfully changed directories since the shell started, or if the
  shell doesn't know where it is.
  .It Ev OPTARG
  When using
  .Ic getopts ,
  it contains the argument for a parsed option, if it requires one.
  .It Ev OPTIND
  The index of the next argument to be processed when using
  .Ic getopts .
  Assigning 1 to this parameter causes
  .Ic getopts
  to process arguments from the beginning the next time it is invoked.
  .It Ev PATH
  A colon separated list of directories that are searched when looking for
  commands and files sourced using the
  .Sq \&.
  command (see below).
  An empty string resulting from a leading or trailing
  colon, or two adjacent colons, is treated as a
  .Sq \&.
  (the current directory).
  .It Ev POSIXLY_CORRECT
  If set, this parameter causes the
  .Ic posix
  option to be enabled.
  See
  .Sx POSIX mode
  below.
  .It Ev PPID
  The process ID of the shell's parent (read-only).
  .It Ev PS1
  The primary prompt for interactive shells.
  Parameter, command, and arithmetic
  substitutions are performed,
  and the prompt string can be customised using
  backslash-escaped special characters.
  .Pp
  Note that since the command-line editors try to figure out how long the prompt
  is (so they know how far it is to the edge of the screen), escape codes in
  the prompt tend to mess things up.
  You can tell the shell not to count certain
  sequences (such as escape codes) by using the
  .Li \e[ Ns Ar ... Ns Li \e]
  substitution (see below) or by prefixing your prompt with a non-printing
  character (such as control-A) followed by a carriage return and then delimiting
  the escape codes with this non-printing character.
  By the way, don't blame me for
  this hack; it's in the original
  .Nm .
  .Pp
  The default prompt is the first part of the hostname, followed by
  .Sq $\ \&
  for non-root users,
  .Sq #\ \&
  for root.
  .Pp
  The following backslash-escaped special characters can be used
  to customise the prompt:
  .Pp
  .Bl -tag -width "\eD{format}XX" -compact
  .It Li \ea
  Insert an ASCII bell character.
  .It Li \ed
  The current date, in the format
  .Dq Day Month Date
  for example
  .Dq Wed Nov 03 .
  .It Li \eD Ns Brq Ar format
  The current date, with
  .Ar format
  converted by
  .Xr strftime 3 .
  The braces must be specified.
  .It Li \ee
  Insert an ASCII escape character.
  .It Li \eh
  The hostname, minus domain name.
  .It Li \eH
  The full hostname, including domain name.
  .It Li \ej
  Current number of jobs running
  (see
  .Sx Job control
  below).
  .It Li \el
  The controlling terminal.
  .It Li \en
  Insert a newline character.
  .It Li \er
  Insert a carriage return character.
  .It Li \es
  The name of the shell.
  .It Li \et
  The current time, in 24-hour HH:MM:SS format.
  .It Li \eT
  The current time, in 12-hour HH:MM:SS format.
  .It Li \e@
  The current time, in 12-hour HH:MM:SS AM/PM format.
  .It Li \eA
  The current time, in 24-hour HH:MM format.
  .It Li \eu
  The current user's username.
  .It Li \ev
  The current version of
  .Nm .
  .It Li \eV
  Like
  .Sq \ev ,
  but more verbose.
  .It Li \ew
  The current working directory.
  .Dv $HOME
  is abbreviated as
  .Sq ~ .
  .It Li \eW
  The basename of
  the current working directory.
  .Dv $HOME
  is abbreviated as
  .Sq ~ .
  .It Li \e!
  The current history number.
  An unescaped
  .Ql !\&
  will produce the current history number too,
  as per the POSIX specification.
  A literal
  .Ql \&!
  can be put in the prompt by placing
  .Ql !!
  in
  .Ev PS1 .
  .It Li \e#
  The current command number.
  This could be different to the current history number,
  if
  .Ev HISTFILE
  contains a history list from a previous session.
  .It Li \e$
  The default prompt character i.e.\&
  .Sq #
  if the effective UID is 0,
  otherwise
  .Sq $ .
  Since the shell interprets
  .Sq $
  as a special character within double quotes,
  it is safer in this case to escape the backslash
  than to try quoting it.
  .It Li \e Ns Ar nnn
  The octal character
  .Ar nnn .
  .It Li \e\e
  Insert a single backslash character.
  .It Li \e[
  Normally the shell keeps track of the number of characters in the prompt.
  Use of this sequence turns off that count.
  .It Li \e]
  Use of this sequence turns the count back on.
  .El
  .Pp
  Note that the backslash itself may be interpreted by the shell.
  Hence, to set
  .Ev PS1
  either escape the backslash itself,
  or use double quotes.
  The latter is more practical:
  .Bd -literal -offset indent
  PS1="\eu "
  .Ed
  .Pp
  This is a more complex example,
  which does not rely on the above backslash-escaped sequences.
  It embeds the current working directory,
  in reverse video,
  in the prompt string:
  .Bd -literal -offset indent
  x=$(print \e\e001)
  PS1="$x$(print \e\er)$x$(tput so)$x\e$PWD$x$(tput se)$x> "
  .Ed
  .It Ev PS2
  Secondary prompt string, by default
  .Sq >\ \& ,
  used when more input is needed to complete a command.
  .It Ev PS3
  Prompt used by the
  .Ic select
  statement when reading a menu selection.
  The default is
  .Sq #?\ \& .
  .It Ev PS4
  Used to prefix commands that are printed during execution tracing (see the
  .Ic set Fl x
  command below).
  Parameter, command, and arithmetic substitutions are performed
  before it is printed.
  The default is
  .Sq +\ \& .
  .It Ev PWD
  The current working directory.
  May be unset or
  .Dv NULL
  if the shell doesn't know where it is.
  .It Ev RANDOM
  A random number generator.
  Every time
  .Ev RANDOM
  is referenced, it is assigned the next random number in the range
  0\-32767.
  By default,
  .Xr arc4random 3
  is used to produce values.
  If the variable
  .Ev RANDOM
  is assigned a value, the value is used as the seed to
  .Xr srand_deterministic 3
  and subsequent references of
  .Ev RANDOM
  produce a predictable sequence.
  .It Ev REPLY
  Default parameter for the
  .Ic read
  command if no names are given.
  Also used in
  .Ic select
  loops to store the value that is read from standard input.
  .It Ev SECONDS
  The number of seconds since the shell started or, if the parameter has been
  assigned an integer value, the number of seconds since the assignment plus the
  value that was assigned.
  .It Ev TERM
  The user's terminal type.
  If set, it will be used to determine the escape sequence used to
  clear the screen.
  .It Ev TMOUT
  If set to a positive integer in an interactive shell, it specifies the maximum
  number of seconds the shell will wait for input after printing the primary
  prompt
  .Pq Ev PS1 .
  If the time is exceeded, the shell exits.
  .It Ev TMPDIR
  The directory temporary shell files are created in.
  If this parameter is not
  set, or does not contain the absolute path of a writable directory, temporary
  files are created in
  .Pa /tmp .
  .It Ev VISUAL
  If set, this parameter controls the command-line editing mode for interactive
  shells.
  If the last component of the path specified in this parameter contains
  the string
  .Dq vi ,
  .Dq emacs ,
  or
  .Dq gmacs ,
  the
  .Xr vi 1 ,
  emacs, or gmacs (Gosling emacs) editing mode is enabled, respectively.
  See also the
  .Ev EDITOR
  parameter, above.
  .El
  .Ss Tilde expansion
  Tilde expansion, which is done in parallel with parameter substitution, is done
  on words starting with an unquoted
  .Ql ~ .
  The characters following the tilde, up to the first
  .Ql / ,
  if any, are assumed to be a login name.
  If the login name is empty,
  .Ql + ,
  or
  .Ql - ,
  the value of the
  .Ev HOME ,
  .Ev PWD ,
  or
  .Ev OLDPWD
  parameter is substituted, respectively.
  Otherwise, the password file is
  searched for the login name, and the tilde expression is substituted with the
  user's home directory.
  If the login name is not found in the password file or
  if any quoting or parameter substitution occurs in the login name, no
  substitution is performed.
  .Pp
  In parameter assignments
  (such as those preceding a simple-command or those occurring
  in the arguments of
  .Ic alias ,
  .Ic export ,
  .Ic readonly ,
  and
  .Ic typeset ) ,
  tilde expansion is done after any assignment
  (i.e. after the equals sign)
  or after an unquoted colon
  .Pq Sq \&: ;
  login names are also delimited by colons.
  .Pp
  The home directory of previously expanded login names are cached and re-used.
  The
  .Ic alias -d
  command may be used to list, change, and add to this cache (e.g.\&
  .Ic alias -d fac=/usr/local/facilities; cd ~fac/bin ) .
  .Ss Brace expansion (alternation)
  Brace expressions take the following form:
  .Bd -unfilled -offset indent
  .Sm off
  .Xo
  .Ar prefix No { Ar str1 No ,...,
  .Ar strN No } Ar suffix
  .Xc
  .Sm on
  .Ed
  .Pp
  The expressions are expanded to
  .Ar N
  words, each of which is the concatenation of
  .Ar prefix ,
  .Ar str Ns i ,
  and
  .Ar suffix
  (e.g.\&
  .Dq a{c,b{X,Y},d}e
  expands to four words:
  .Dq ace ,
  .Dq abXe ,
  .Dq abYe ,
  and
  .Dq ade ) .
  As noted in the example, brace expressions can be nested and the resulting
  words are not sorted.
  Brace expressions must contain an unquoted comma
  .Pq Sq \&,
  for expansion to occur (e.g.\&
  .Ic {}
  and
  .Ic {foo}
  are not expanded).
  Brace expansion is carried out after parameter substitution
  and before file name generation.
  .Ss File name patterns
  A file name pattern is a word containing one or more unquoted
  .Ql \&? ,
  .Ql * ,
  .Ql + ,
  .Ql @ ,
  or
  .Ql \&!
  characters or
  .Dq [..]
  sequences.
  Once brace expansion has been performed, the shell replaces file
  name patterns with the sorted names of all the files that match the pattern
  (if no files match, the word is left unchanged).
  The pattern elements have the following meaning:
  .Bl -tag -width Ds
  .It \&?
  Matches any single character.
  .It \&*
  Matches any sequence of characters.
  .It [..]
  Matches any of the characters inside the brackets.
  Ranges of characters can be
  specified by separating two characters by a
  .Ql -
  (e.g.\&
  .Dq [a0-9]
  matches the letter
  .Sq a
  or any digit).
  In order to represent itself, a
  .Ql -
  must either be quoted or the first or last character in the character list.
  Similarly, a
  .Ql \&]
  must be quoted or the first character in the list if it is to represent itself
  instead of the end of the list.
  Also, a
  .Ql \&!
  appearing at the start of the list has special meaning (see below), so to
  represent itself it must be quoted or appear later in the list.
  .Pp
  Within a bracket expression, the name of a
  .Em character class
  enclosed in
  .Sq [:
  and
  .Sq :]
  stands for the list of all characters belonging to that class.
  Supported character classes:
  .Bd -literal -offset indent
  alnum	cntrl	lower	space
  alpha	digit	print	upper
  blank	graph	punct	xdigit
  .Ed
  .Pp
  These match characters using the macros specified in
  .Xr isalnum 3 ,
  .Xr isalpha 3 ,
  and so on.
  A character class may not be used as an endpoint of a range.
  .It [!..]
  Like [..],
  except it matches any character not inside the brackets.
  .Sm off
  .It *( Ar pattern Ns | No ...| Ar pattern )
  .Sm on
  Matches any string of characters that matches zero or more occurrences of the
  specified patterns.
  Example: The pattern
  .Ic *(foo|bar)
  matches the strings
  .Dq ,
  .Dq foo ,
  .Dq bar ,
  .Dq foobarfoo ,
  etc.
  .Sm off
  .It +( Ar pattern Ns | No ...| Ar pattern )
  .Sm on
  Matches any string of characters that matches one or more occurrences of the
  specified patterns.
  Example: The pattern
  .Ic +(foo|bar)
  matches the strings
  .Dq foo ,
  .Dq bar ,
  .Dq foobar ,
  etc.
  .Sm off
  .It ?( Ar pattern Ns | No ...| Ar pattern )
  .Sm on
  Matches the empty string or a string that matches one of the specified
  patterns.
  Example: The pattern
  .Ic ?(foo|bar)
  only matches the strings
  .Dq ,
  .Dq foo ,
  and
  .Dq bar .
  .Sm off
  .It @( Ar pattern Ns | No ...| Ar pattern )
  .Sm on
  Matches a string that matches one of the specified patterns.
  Example: The pattern
  .Ic @(foo|bar)
  only matches the strings
  .Dq foo
  and
  .Dq bar .
  .Sm off
  .It !( Ar pattern Ns | No ...| Ar pattern )
  .Sm on
  Matches any string that does not match one of the specified patterns.
  Examples: The pattern
  .Ic !(foo|bar)
  matches all strings except
  .Dq foo
  and
  .Dq bar ;
  the pattern
  .Ic !(*)
  matches no strings; the pattern
  .Ic !(?)*\&
  matches all strings (think about it).
  .El
  .Pp
  Unlike most shells,
  .Nm ksh
  never matches
  .Sq \&.
  and
  .Sq .. .
  .Pp
  Note that none of the above pattern elements match either a period
  .Pq Sq \&.
  at the start of a file name or a slash
  .Pq Sq / ,
  even if they are explicitly used in a [..] sequence; also, the names
  .Sq \&.
  and
  .Sq ..
  are never matched, even by the pattern
  .Sq .* .
  .Pp
  If the
  .Ic markdirs
  option is set, any directories that result from file name generation are marked
  with a trailing
  .Ql / .
  .Ss Input/output redirection
  When a command is executed, its standard input, standard output, and standard
  error (file descriptors 0, 1, and 2, respectively) are normally inherited from
  the shell.
  Three exceptions to this are commands in pipelines, for which
  standard input and/or standard output are those set up by the pipeline,
  asynchronous commands created when job control is disabled, for which standard
  input is initially set to be from
  .Pa /dev/null ,
  and commands for which any of the following redirections have been specified:
  .Bl -tag -width Ds
  .It Cm > Ar file
  Standard output is redirected to
  .Ar file .
  If
  .Ar file
  does not exist, it is created; if it does exist, is a regular file, and the
  .Ic noclobber
  option is set, an error occurs; otherwise, the file is truncated.
  Note that this means the command
  .Ic cmd < foo > foo
  will open
  .Ar foo
  for reading and then truncate it when it opens it for writing, before
  .Ar cmd
  gets a chance to actually read
  .Ar foo .
  .It Cm >| Ar file
  Same as
  .Cm > ,
  except the file is truncated, even if the
  .Ic noclobber
  option is set.
  .It Cm >> Ar file
  Same as
  .Cm > ,
  except if
  .Ar file
  exists it is appended to instead of being truncated.
  Also, the file is opened
  in append mode, so writes always go to the end of the file (see
  .Xr open 2 ) .
  .It Cm < Ar file
  Standard input is redirected from
  .Ar file ,
  which is opened for reading.
  .It Cm <> Ar file
  Same as
  .Cm < ,
  except the file is opened for reading and writing.
  .It Cm << Ar marker
  After reading the command line containing this kind of redirection (called a
  .Dq here document ) ,
  the shell copies lines from the command source into a temporary file until a
  line matching
  .Ar marker
  is read.
  When the command is executed, standard input is redirected from the
  temporary file.
  If
  .Ar marker
  contains no quoted characters, the contents of the temporary file are processed
  as if enclosed in double quotes each time the command is executed, so
  parameter, command, and arithmetic substitutions are performed, along with
  backslash
  .Pq Sq \e
  escapes for
  .Ql $ ,
  .Ql ` ,
  .Ql \e ,
  and
  .Ql \enewline .
  If multiple here documents are used on the same command line, they are saved in
  order.
  .It Cm <<- Ar marker
  Same as
  .Cm << ,
  except leading tabs are stripped from lines in the here document.
  .It Cm <& Ar fd
  Standard input is duplicated from file descriptor
  .Ar fd .
  .Ar fd
  can be a single digit, indicating the number of an existing file descriptor;
  the letter
  .Ql p ,
  indicating the file descriptor associated with the output of the current
  co-process; or the character
  .Ql - ,
  indicating standard input is to be closed.
  .It Cm >& Ar fd
  Same as
  .Cm <& ,
  except the operation is done on standard output.
  .El
  .Pp
  In any of the above redirections, the file descriptor that is redirected
  (i.e. standard input or standard output)
  can be explicitly given by preceding the
  redirection with a single digit.
  Parameter, command, and arithmetic
  substitutions, tilde substitutions, and (if the shell is interactive)
  file name generation are all performed on the
  .Ar file ,
  .Ar marker ,
  and
  .Ar fd
  arguments of redirections.
  Note, however, that the results of any file name
  generation are only used if a single file is matched; if multiple files match,
  the word with the expanded file name generation characters is used.
  Note
  that in restricted shells, redirections which can create files cannot be used.
  .Pp
  For simple-commands, redirections may appear anywhere in the command; for
  compound-commands
  .Po
  .Ic if
  statements, etc.
  .Pc ,
  any redirections must appear at the end.
  Redirections are processed after
  pipelines are created and in the order they are given, so the following
  will print an error with a line number prepended to it:
  .Pp
  .D1 $ cat /foo/bar 2>&1 > /dev/null | cat -n
  .Ss Arithmetic expressions
  Integer arithmetic expressions can be used with the
  .Ic let
  command, inside $((..)) expressions, inside array references (e.g.\&
  .Ar name Ns Bq Ar expr ) ,
  as numeric arguments to the
  .Ic test
  command, and as the value of an assignment to an integer parameter.
  .Pp
  Expressions may contain alpha-numeric parameter identifiers, array references,
  and integer constants and may be combined with the following C operators
  (listed and grouped in increasing order of precedence):
  .Pp
  Unary operators:
  .Bd -literal -offset indent
  + - ! ~ ++ --
  .Ed
  .Pp
  Binary operators:
  .Bd -literal -offset indent
  ,
  = *= /= %= += -= <<= >>= &= ^= |=
  ||
  &&
  |
  ^
  &
  == !=
  < <= >= >
  << >>
  + -
  * / %
  .Ed
  .Pp
  Ternary operators:
  .Bd -literal -offset indent
  ?: (precedence is immediately higher than assignment)
  .Ed
  .Pp
  Grouping operators:
  .Bd -literal -offset indent
  ( )
  .Ed
  .Pp
  A parameter that is NULL or unset evaluates to 0.
  Integer constants may be specified with arbitrary bases using the notation
  .Ar base Ns # Ns Ar number ,
  where
  .Ar base
  is a decimal integer specifying the base, and
  .Ar number
  is a number in the specified base.
  Additionally,
  integers may be prefixed with
  .Sq 0X
  or
  .Sq 0x
  (specifying base 16)
  or
  .Sq 0
  (base 8)
  in all forms of arithmetic expressions,
  except as numeric arguments to the
  .Ic test
  command.
  .Pp
  The operators are evaluated as follows:
  .Bl -tag -width Ds -offset indent
  .It unary +
  Result is the argument (included for completeness).
  .It unary -
  Negation.
  .It \&!
  Logical NOT;
  the result is 1 if argument is zero, 0 if not.
  .It ~
  Arithmetic (bit-wise) NOT.
  .It ++
  Increment; must be applied to a parameter (not a literal or other expression).
  The parameter is incremented by 1.
  When used as a prefix operator, the result
  is the incremented value of the parameter; when used as a postfix operator, the
  result is the original value of the parameter.
  .It --
  Similar to
  .Ic ++ ,
  except the parameter is decremented by 1.
  .It \&,
  Separates two arithmetic expressions; the left-hand side is evaluated first,
  then the right.
  The result is the value of the expression on the right-hand side.
  .It =
  Assignment; the variable on the left is set to the value on the right.
  .It Xo
  .No *= /= += -= <<=
  .No >>= &= ^= |=
  .Xc
  Assignment operators.
  .Sm off
  .Ao Ar var Ac Xo
  .Aq Ar op
  .No = Aq Ar expr
  .Xc
  .Sm on
  is the same as
  .Sm off
  .Ao Ar var Ac Xo
  .No = Aq Ar var
  .Aq Ar op
  .Aq Ar expr ,
  .Xc
  .Sm on
  with any operator precedence in
  .Aq Ar expr
  preserved.
  For example,
  .Dq var1 *= 5 + 3
  is the same as specifying
  .Dq var1 = var1 * (5 + 3) .
  .It ||
  Logical OR;
  the result is 1 if either argument is non-zero, 0 if not.
  The right argument is evaluated only if the left argument is zero.
  .It &&
  Logical AND;
  the result is 1 if both arguments are non-zero, 0 if not.
  The right argument is evaluated only if the left argument is non-zero.
  .It |
  Arithmetic (bit-wise) OR.
  .It ^
  Arithmetic (bit-wise) XOR
  (exclusive-OR).
  .It &
  Arithmetic (bit-wise) AND.
  .It ==
  Equal; the result is 1 if both arguments are equal, 0 if not.
  .It !=
  Not equal; the result is 0 if both arguments are equal, 1 if not.
  .It <
  Less than; the result is 1 if the left argument is less than the right, 0 if
  not.
  .It <= >= >
  Less than or equal, greater than or equal, greater than.
  See
  .Ic < .
  .It << >>
  Shift left (right); the result is the left argument with its bits shifted left
  (right) by the amount given in the right argument.
  .It + - * /
  Addition, subtraction, multiplication, and division.
  .It %
  Remainder; the result is the remainder of the division of the left argument by
  the right.
  The sign of the result is unspecified if either argument is negative.
  .It Xo
  .Sm off
  .Aq Ar arg1 ?
  .Aq Ar arg2 :
  .Aq Ar arg3
  .Sm on
  .Xc
  If
  .Aq Ar arg1
  is non-zero, the result is
  .Aq Ar arg2 ;
  otherwise the result is
  .Aq Ar arg3 .
  .El
  .Ss Co-processes
  A co-process, which is a pipeline created with the
  .Sq |&
  operator, is an asynchronous process that the shell can both write to (using
  .Ic print -p )
  and read from (using
  .Ic read -p ) .
  The input and output of the co-process can also be manipulated using
  .Cm >&p
  and
  .Cm <&p
  redirections, respectively.
  Once a co-process has been started, another can't
  be started until the co-process exits, or until the co-process's input has been
  redirected using an
  .Ic exec Ar n Ns Cm >&p
  redirection.
  If a co-process's input is redirected in this way, the next
  co-process to be started will share the output with the first co-process,
  unless the output of the initial co-process has been redirected using an
  .Ic exec Ar n Ns Cm <&p
  redirection.
  .Pp
  Some notes concerning co-processes:
  .Bl -bullet
  .It
  The only way to close the co-process's input (so the co-process reads an
  end-of-file) is to redirect the input to a numbered file descriptor and then
  close that file descriptor e.g.\&
  .Ic exec 3>&p; exec 3>&- .
  .It
  In order for co-processes to share a common output, the shell must keep the
  write portion of the output pipe open.
  This means that end-of-file will not be
  detected until all co-processes sharing the co-process's output have exited
  (when they all exit, the shell closes its copy of the pipe).
  This can be
  avoided by redirecting the output to a numbered file descriptor (as this also
  causes the shell to close its copy).
  Note that this behaviour is slightly
  different from the original Korn shell which closes its copy of the write
  portion of the co-process output when the most recently started co-process
  (instead of when all sharing co-processes) exits.
  .It
  .Ic print -p
  will ignore
  .Dv SIGPIPE
  signals during writes if the signal is not being trapped or ignored; the same
  is true if the co-process input has been duplicated to another file descriptor
  and
  .Ic print -u Ns Ar n
  is used.
  .El
  .Ss Functions
  Functions are defined using either Korn shell
  .Ic function Ar function-name
  syntax or the Bourne/POSIX shell
  .Ar function-name Ns ()
  syntax (see below for the difference between the two forms).
  Functions are like
  .Li .-scripts
  (i.e. scripts sourced using the
  .Sq \&.
  built-in)
  in that they are executed in the current environment.
  However, unlike
  .Li .-scripts ,
  shell arguments (i.e. positional parameters $1, $2, etc.)\&
  are never visible inside them.
  When the shell is determining the location of a command, functions
  are searched after special built-in commands, before regular and
  non-regular built-ins, and before the
  .Ev PATH
  is searched.
  .Pp
  An existing function may be deleted using
  .Ic unset Fl f Ar function-name .
  A list of functions can be obtained using
  .Ic typeset +f
  and the function definitions can be listed using
  .Ic typeset -f .
  The
  .Ic autoload
  command (which is an alias for
  .Ic typeset -fu )
  may be used to create undefined functions: when an undefined function is
  executed, the shell searches the path specified in the
  .Ev FPATH
  parameter for a file with the same name as the function, which, if found, is
  read and executed.
  If after executing the file the named function is found to
  be defined, the function is executed; otherwise, the normal command search is
  continued (i.e. the shell searches the regular built-in command table and
  .Ev PATH ) .
  Note that if a command is not found using
  .Ev PATH ,
  an attempt is made to autoload a function using
  .Ev FPATH
  (this is an undocumented feature of the original Korn shell).
  .Pp
  Functions can have two attributes,
  .Dq trace
  and
  .Dq export ,
  which can be set with
  .Ic typeset -ft
  and
  .Ic typeset -fx ,
  respectively.
  When a traced function is executed, the shell's
  .Ic xtrace
  option is turned on for the function's duration; otherwise, the
  .Ic xtrace
  option is turned off.
  The
  .Dq export
  attribute of functions is currently not used.
  In the original Korn shell,
  exported functions are visible to shell scripts that are executed.
  .Pp
  Since functions are executed in the current shell environment, parameter
  assignments made inside functions are visible after the function completes.
  If this is not the desired effect, the
  .Ic typeset
  command can be used inside a function to create a local parameter.
  Note that special parameters (e.g.\&
  .Ic \&$$ , $! )
  can't be scoped in this way.
  .Pp
  The exit status of a function is that of the last command executed in the
  function.
  A function can be made to finish immediately using the
  .Ic return
  command; this may also be used to explicitly specify the exit status.
  .Pp
  Functions defined with the
  .Ic function
  reserved word are treated differently in the following ways from functions
  defined with the
  .Ic ()
  notation:
  .Bl -bullet
  .It
  The $0 parameter is set to the name of the function
  (Bourne-style functions leave $0 untouched).
  .It
  Parameter assignments preceding function calls are not kept in the shell
  environment (executing Bourne-style functions will keep assignments).
  .It
  .Ev OPTIND
  is saved/reset and restored on entry and exit from the function so
  .Ic getopts
  can be used properly both inside and outside the function (Bourne-style
  functions leave
  .Ev OPTIND
  untouched, so using
  .Ic getopts
  inside a function interferes with using
  .Ic getopts
  outside the function).
  .El
  .Ss POSIX mode
  The shell is intended to be POSIX compliant;
  however, in some cases, POSIX behaviour is contrary either to
  the original Korn shell behaviour or to user convenience.
  How the shell behaves in these cases is determined by the state of the
  .Ic posix
  option
  .Pq Ic set -o posix .
  If it is on, the POSIX behaviour is followed; otherwise, it is not.
  The
  .Ic posix
  option is set automatically when the shell starts up if the environment
  contains the
  .Ev POSIXLY_CORRECT
  parameter.
  The shell can also be compiled so that it is in POSIX mode by default;
  however, this is usually not desirable.
  .Pp
  The following is a list of things that are affected by the state of the
  .Ic posix
  option:
  .Bl -bullet
  .It
  .Ic kill -l
  output.
  In POSIX mode, only signal names are listed (in a single line);
  in non-POSIX mode,
  signal numbers, names, and descriptions are printed (in columns).
  .It
  .Ic echo
  options.
  In POSIX mode,
  .Fl e
  and
  .Fl E
  are not treated as options, but printed like other arguments;
  in non-POSIX mode, these options control the interpretation
  of backslash sequences.
  .It
  .Ic fg
  exit status.
  In POSIX mode, the exit status is 0 if no errors occur;
  in non-POSIX mode, the exit status is that of the last foregrounded job.
  .It
  .Ic eval
  exit status.
  If
  .Ic eval
  gets to see an empty command (i.e.\&
  .Ic eval `false` ) ,
  its exit status in POSIX mode will be 0.
  In non-POSIX mode,
  it will be the exit status of the last command substitution that was
  done in the processing of the arguments to
  .Ic eval
  (or 0 if there were no command substitutions).
  .It
  .Ic getopts .
  In POSIX mode, options must start with a
  .Ql - ;
  in non-POSIX mode, options can start with either
  .Ql -
  or
  .Ql + .
  .It
  Brace expansion (also known as alternation).
  In POSIX mode, brace expansion is disabled;
  in non-POSIX mode, brace expansion is enabled.
  Note that
  .Ic set -o posix
  (or setting the
  .Ev POSIXLY_CORRECT
  parameter) automatically turns the
  .Ic braceexpand
  option off; however, it can be explicitly turned on later.
  .It
  .Ic set - .
  In POSIX mode, this does not clear the
  .Ic verbose
  or
  .Ic xtrace
  options; in non-POSIX mode, it does.
  .It
  .Ic set
  exit status.
  In POSIX mode, the exit status of
  .Ic set
  is 0 if there are no errors;
  in non-POSIX mode, the exit status is that of any
  command substitutions performed in generating the
  .Ic set
  command.
  For example,
  .Ic set -- `false`; echo $?\&
  prints 0 in POSIX mode, 1 in non-POSIX mode.
  This construct is used in most shell scripts that use the old
  .Xr getopt 1
  command.
  .It
  Argument expansion of the
  .Ic alias ,
  .Ic export ,
  .Ic readonly ,
  and
  .Ic typeset
  commands.
  In POSIX mode, normal argument expansion is done; in non-POSIX mode,
  field splitting, file globbing, brace expansion, and (normal) tilde expansion
  are turned off, while assignment tilde expansion is turned on.
  .It
  Signal specification.
  In POSIX mode, signals can be specified as digits, only
  if signal numbers match POSIX values
  (i.e. HUP=1, INT=2, QUIT=3, ABRT=6, KILL=9, ALRM=14, and TERM=15);
  in non-POSIX mode, signals can always be digits.
  .It
  Alias expansion.
  In POSIX mode, alias expansion is only carried out when reading command words;
  in non-POSIX mode, alias expansion is carried out on any
  word following an alias that ended in a space.
  For example, the following
  .Ic for
  loop uses parameter
  .Sq i
  in POSIX mode and
  .Sq j
  in non-POSIX mode:
  .Bd -literal -offset indent
  alias a='for ' i='j'
  a i in 1 2; do echo i=$i j=$j; done
  .Ed
  .It
  .Ic test .
  In POSIX mode, the expression
  .Sq Fl t
  (preceded by some number of
  .Sq \&!
  arguments) is always true as it is a non-zero length string;
  in non-POSIX mode, it tests if file descriptor 1 is a
  .Xr tty 4
  (i.e. the
  .Ar fd
  argument to the
  .Fl t
  test may be left out and defaults to 1).
  .El
  .Ss Strict Bourne shell mode
  When the
  .Ic sh
  option is enabled (see the
  .Ic set
  command),
  .Nm
  will behave like
  .Xr sh 1
  in the following ways:
  .Bl -bullet
  .It
  The parameter
  .Ic $_
  is not set to:
  .Pp
  .Bl -dash -compact
  .It
  the expanded alias' full program path after entering commands
  that are tracked aliases
  .It
  the last argument on the command line after entering external
  commands
  .It
  the file that changed when
  .Ev MAILPATH
  is set to monitor a mailbox
  .El
  .It
  File descriptors are left untouched when executing
  .Ic exec
  with no arguments.
  .It
  Backslash-escaped special characters are not substituted in
  .Ev PS1 .
  .It
  Sequences of
  .Sq ((...))
  are not interpreted as arithmetic expressions.
  .El
  .Ss Command execution
  After evaluation of command-line arguments, redirections, and parameter
  assignments, the type of command is determined: a special built-in, a
  function, a regular built-in, or the name of a file to execute found using the
  .Ev PATH
  parameter.
  The checks are made in the above order.
  Special built-in commands differ from other commands in that the
  .Ev PATH
  parameter is not used to find them, an error during their execution can
  cause a non-interactive shell to exit, and parameter assignments that are
  specified before the command are kept after the command completes.
  Just to confuse things, if the
  .Ic posix
  option is turned off (see the
  .Ic set
  command below), some special commands are very special in that no field
  splitting, file globbing, brace expansion, nor tilde expansion is performed
  on arguments that look like assignments.
  Regular built-in commands are different only in that the
  .Ev PATH
  parameter is not used to find them.
  .Pp
  The original
  .Nm ksh
  and POSIX differ somewhat in which commands are considered
  special or regular:
  .Pp
  POSIX special commands
  .Pp
  .Ic \&. , \&: , break , continue ,
  .Ic eval , exec , exit , export ,
  .Ic readonly , return , set , shift ,
  .Ic times , trap , unset
  .Pp
  Additional
  .Nm
  special commands
  .Pp
  .Ic builtin , typeset
  .Pp
  Very special commands
  .Pq when POSIX mode is off
  .Pp
  .Ic alias , readonly , set , typeset
  .Pp
  POSIX regular commands
  .Pp
  .Ic alias , bg , cd , command ,
  .Ic false , fc , fg , getopts ,
  .Ic jobs , kill , pwd , read ,
  .Ic true , umask , unalias , wait
  .Pp
  Additional
  .Nm
  regular commands
  .Pp
  .Ic \&[ , echo , let ,
  .Ic print , suspend , test ,
  .Ic ulimit , whence
  .Pp
  Once the type of command has been determined, any command-line parameter
  assignments are performed and exported for the duration of the command.
  .Pp
  The following describes the special and regular built-in commands:
  .Pp
  .Bl -tag -width Ds -compact
  .It Ic \&. Ar file Op Ar arg ...
  Execute the commands in
  .Ar file
  in the current environment.
  The file is searched for in the directories of
  .Ev PATH .
  If arguments are given, the positional parameters may be used to access them
  while
  .Ar file
  is being executed.
  If no arguments are given, the positional parameters are
  those of the environment the command is used in.
  .Pp
  .It Ic \&: Op Ar ...
  The null command.
  Exit status is set to zero.
  .Pp
  .It Xo Ic alias
  .Oo Fl d | t Oo Fl r Oc |
  .Cm +-x Oc
  .Op Fl p
  .Op Cm +
  .Oo Ar name
  .Op Ns = Ns Ar value
  .Ar ... Oc
  .Xc
  Without arguments,
  .Ic alias
  lists all aliases.
  For any name without a value, the existing alias is listed.
  Any name with a value defines an alias (see
  .Sx Aliases
  above).
  .Pp
  When listing aliases, one of two formats is used.
  Normally, aliases are listed as
  .Ar name Ns = Ns Ar value ,
  where
  .Ar value
  is quoted.
  If options were preceded with
  .Ql + ,
  or a lone
  .Ql +
  is given on the command line, only
  .Ar name
  is printed.
  .Pp
  The
  .Fl d
  option causes directory aliases, which are used in tilde expansion, to be
  listed or set (see
  .Sx Tilde expansion
  above).
  .Pp
  If the
  .Fl p
  option is used, each alias is prefixed with the string
  .Dq alias\ \& .
  .Pp
  The
  .Fl t
  option indicates that tracked aliases are to be listed/set (values specified on
  the command line are ignored for tracked aliases).
  The
  .Fl r
  option indicates that all tracked aliases are to be reset.
  .Pp
  The
  .Fl x
  option sets
  .Pq Ic +x No clears
  the export attribute of an alias or, if no names are given, lists the aliases
  with the export attribute (exporting an alias has no effect).
  .Pp
  .It Ic bg Op Ar job ...
  Resume the specified stopped job(s) in the background.
  If no jobs are specified,
  .Ic %+
  is assumed.
  See
  .Sx Job control
  below for more information.
  .Pp
  .It Ic bind Op Fl l
  The current bindings are listed.
  If the
  .Fl l
  flag is given,
  .Ic bind
  instead lists the names of the functions to which keys may be bound.
  See
  .Sx Emacs editing mode
  for more information.
  .Pp
  .It Xo Ic bind Op Fl m
  .Ar string Ns = Ns Op Ar substitute
  .Ar ...
  .Xc
  .It Xo Ic bind
  .Ar string Ns = Ns Op Ar editing-command
  .Ar ...
  .Xc
  In
  .Sx Emacs editing mode ,
  the specified editing command is bound to the given
  .Ar string .
  Future input of the
  .Ar string
  will cause the editing command to be immediately invoked.
  Bindings have no effect in
  .Sx Vi editing mode .
  .Pp
  If the
  .Fl m
  flag is given, the specified input
  .Ar string
  will afterwards be immediately replaced by the given
  .Ar substitute
  string, which may contain editing commands.
  Control characters may be written using caret notation.
  For example, ^X represents Control-X.
  .Pp
  If a certain character occurs as the first character of any bound
  multi-character
  .Ar string
  sequence, that character becomes a command prefix character.
  Any character sequence that starts with a command prefix character
  but that is not bound to a command or substitute
  is implicitly considered as bound to the
  .Sq error
  command.
  By default, two command prefix characters exist:
  Escape
  .Pq ^[
  and Control-X
  .Pq ^X .
  .Pp
  The following default bindings show how the arrow keys
  on an ANSI terminal or xterm are bound
  (of course some escape sequences won't work out quite this nicely):
  .Bd -literal -offset indent
  bind '^[[A'=up-history
  bind '^[[B'=down-history
  bind '^[[C'=forward-char
  bind '^[[D'=backward-char
  .Ed
  .Pp
  .It Ic break Op Ar level
  Exit the
  .Ar level Ns th
  inner-most
  .Ic for ,
  .Ic select ,
  .Ic until ,
  or
  .Ic while
  loop.
  .Ar level
  defaults to 1.
  .Pp
  .It Ic builtin Ar command Op Ar arg ...
  Execute the built-in command
  .Ar command .
  .Pp
  .It Xo
  .Ic cd
  .Op Fl LP
  .Op Ar dir
  .Xc
  Set the working directory to
  .Ar dir .
  If the parameter
  .Ev CDPATH
  is set, it lists the search path for the directory containing
  .Ar dir .
  A
  .Dv NULL
  path or
  .Ql .\&
  means the current directory.
  If
  .Ar dir
  is found in any component of the
  .Ev CDPATH
  search path other than the
  .Dv NULL
  path, the name of the new working directory will be written to standard output.
  If
  .Ar dir
  is missing, the home directory
  .Ev HOME
  is used.
  If
  .Ar dir
  is
  .Ql - ,
  the previous working directory is used (see the
  .Ev OLDPWD
  parameter).
  .Pp
  If the
  .Fl L
  option (logical path) is used or if the
  .Ic physical
  option isn't set (see the
  .Ic set
  command below), references to
  .Sq ..
  in
  .Ar dir
  are relative to the path used to get to the directory.
  If the
  .Fl P
  option (physical path) is used or if the
  .Ic physical
  option is set,
  .Sq ..
  is relative to the filesystem directory tree.
  The
  .Ev PWD
  and
  .Ev OLDPWD
  parameters are updated to reflect the current and old working directory,
  respectively.
  .Pp
  .It Xo
  .Ic cd
  .Op Fl LP
  .Ar old new
  .Xc
  The string
  .Ar new
  is substituted for
  .Ar old
  in the current directory, and the shell attempts to change to the new
  directory.
  .Pp
  .It Xo
  .Ic command
  .Op Fl pVv
  .Ar cmd
  .Op Ar arg ...
  .Xc
  If neither the
  .Fl v
  nor
  .Fl V
  option is given,
  .Ar cmd
  is executed exactly as if
  .Ic command
  had not been specified, with two exceptions:
  firstly,
  .Ar cmd
  cannot be an alias or a shell function;
  and secondly, special built-in commands lose their specialness
  (i.e. redirection and utility errors do not cause the shell to
  exit, and command assignments are not permanent).
  .Pp
  If the
  .Fl p
  option is given, a default search path is used instead of the current value of
  .Ev PATH
  (the actual value of the default path is system dependent: on
  POSIX-ish systems, it is the value returned by
  .Ic getconf PATH ) .
  Nevertheless, reserved words, aliases, shell functions, and
  builtin commands are still found before external commands.
  .Pp
  If the
  .Fl v
  option is given, instead of executing
  .Ar cmd ,
  information about what would be executed is given (and the same is done for
  .Ar arg ... ) .
  For special and regular built-in commands and functions, their names are simply
  printed; for aliases, a command that defines them is printed; and for commands
  found by searching the
  .Ev PATH
  parameter, the full path of the command is printed.
  If no command is found
  (i.e. the path search fails), nothing is printed and
  .Ic command
  exits with a non-zero status.
  The
  .Fl V
  option is like the
  .Fl v
  option, except it is more verbose.
  .Pp
  .It Ic continue Op Ar level
  Jumps to the beginning of the
  .Ar level Ns th
  inner-most
  .Ic for ,
  .Ic select ,
  .Ic until ,
  or
  .Ic while
  loop.
  .Ar level
  defaults to 1.
  .Pp
  .It Xo
  .Ic echo
  .Op Fl Een
  .Op Ar arg ...
  .Xc
  Prints its arguments (separated by spaces) followed by a newline, to the
  standard output.
  The newline is suppressed if any of the arguments contain the
  backslash sequence
  .Ql \ec .
  See the
  .Ic print
  command below for a list of other backslash sequences that are recognized.
  .Pp
  The options are provided for compatibility with
  .Bx
  shell scripts.
  The
  .Fl n
  option suppresses the trailing newline,
  .Fl e
  enables backslash interpretation (a no-op, since this is normally done), and
  .Fl E
  suppresses backslash interpretation.
  If the
  .Ic posix
  option is set, only the first argument is treated as an option, and only
  if it is exactly
  .Dq -n .
  .Pp
  .It Ic eval Ar command ...
  The arguments are concatenated (with spaces between them) to form a single
  string which the shell then parses and executes in the current environment.
  .Pp
  .It Xo
  .Ic exec
  .Op Ar command Op Ar arg ...
  .Xc
  The command is executed without forking, replacing the shell process.
  .Pp
  If no command is given except for I/O redirection, the I/O redirection is
  permanent and the shell is
  not replaced.
  Any file descriptors greater than 2 which are opened or
  .Xr dup 2 Ns 'd
  in this way are not made available to other executed commands (i.e. commands
  that are not built-in to the shell).
  Note that the Bourne shell differs here;
  it does pass these file descriptors on.
  .Pp
  .It Ic exit Op Ar status
  The shell exits with the specified exit status.
  If
  .Ar status
  is not specified, the exit status is the current value of the
  .Ic $?\&
  parameter.
  .Pp
  .It Xo
  .Ic export
  .Op Fl p
  .Op Ar parameter Ns Op = Ns Ar value
  .Xc
  Sets the export attribute of the named parameters.
  Exported parameters are passed in the environment to executed commands.
  If values are specified, the named parameters are also assigned.
  .Pp
  If no parameters are specified, the names of all parameters with the export
  attribute are printed one per line, unless the
  .Fl p
  option is used, in which case
  .Ic export
  commands defining all exported parameters, including their values, are printed.
  .Pp
  .It Ic false
  A command that exits with a non-zero status.
  .Pp
  .It Xo
  .Ic fc
  .Oo
  .Fl e Ar editor |
  .Fl l Op Fl n
  .Oc
  .Op Fl r
  .Op Ar first Op Ar last
  .Xc
  Fix command.
  .Ar first
  and
  .Ar last
  select commands from the history.
  Commands can be selected by history number
  or a string specifying the most recent command starting with that string.
  The
  .Fl l
  option lists the command on standard output, and
  .Fl n
  inhibits the default command numbers.
  The
  .Fl r
  option reverses the order of the list.
  Without
  .Fl l ,
  the selected commands are edited by the editor specified with the
  .Fl e
  option, or if no
  .Fl e
  is specified, the editor specified by the
  .Ev FCEDIT
  parameter (if this parameter is not set,
  .Pa /bin/ed
  is used), and then executed by the shell.
  .Pp
  .It Xo
  .Ic fc Fl s
  .Op Fl g
  .Op Ar old Ns = Ns Ar new
  .Op Ar prefix
  .Xc
  Re-execute the most recent command beginning with
  .Ar prefix ,
  or the previous command if no
  .Ar prefix
  is specified,
  performing the optional substitution of
  .Ar old
  with
  .Ar new .
  If
  .Fl g
  is specified, all occurrences of
  .Ar old
  are replaced with
  .Ar new .
  The editor is not invoked when the
  .Fl s
  flag is used.
  The obsolescent equivalent
  .Dq Fl e No -
  is also accepted.
  This command is usually accessed with the predefined
  .Ic alias r='fc -s' .
  .Pp
  .It Ic fg Op Ar job ...
  Resume the specified job(s) in the foreground.
  If no jobs are specified,
  .Ic %+
  is assumed.
  See
  .Sx Job control
  below for more information.
  .Pp
  .It Xo
  .Ic getopts
  .Ar optstring name
  .Op Ar arg ...
  .Xc
  Used by shell procedures to parse the specified arguments (or positional
  parameters, if no arguments are given) and to check for legal options.
  .Ar optstring
  contains the option letters that
  .Ic getopts
  is to recognize.
  If a letter is followed by a colon, the option is expected to
  have an argument.
  Options that do not take arguments may be grouped in a single argument.
  If an option takes an argument and the option character is not the
  last character of the argument it is found in, the remainder of the argument is
  taken to be the option's argument; otherwise, the next argument is the option's
  argument.
  .Pp
  Each time
  .Ic getopts
  is invoked, it places the next option in the shell parameter
  .Ar name
  and the index of the argument to be processed by the next call to
  .Ic getopts
  in the shell parameter
  .Ev OPTIND .
  If the option was introduced with a
  .Ql + ,
  the option placed in
  .Ar name
  is prefixed with a
  .Ql + .
  When an option requires an argument,
  .Ic getopts
  places it in the shell parameter
  .Ev OPTARG .
  .Pp
  When an illegal option or a missing option argument is encountered, a question
  mark or a colon is placed in
  .Ar name
  (indicating an illegal option or missing argument, respectively) and
  .Ev OPTARG
  is set to the option character that caused the problem.
  Furthermore, if
  .Ar optstring
  does not begin with a colon, a question mark is placed in
  .Ar name ,
  .Ev OPTARG
  is unset, and an error message is printed to standard error.
  .Pp
  When the end of the options is encountered,
  .Ic getopts
  exits with a non-zero exit status.
  Options end at the first (non-option
  argument) argument that does not start with a
  .Ql - ,
  or when a
  .Ql --
  argument is encountered.
  .Pp
  Option parsing can be reset by setting
  .Ev OPTIND
  to 1 (this is done automatically whenever the shell or a shell procedure is
  invoked).
  .Pp
  Warning: Changing the value of the shell parameter
  .Ev OPTIND
  to a value other than 1, or parsing different sets of arguments without
  resetting
  .Ev OPTIND ,
  may lead to unexpected results.
  .Pp
  .It Xo
  .Ic hash
  .Op Fl r
  .Op Ar name ...
  .Xc
  Without arguments, any hashed executable command pathnames are listed.
  The
  .Fl r
  option causes all hashed commands to be removed from the hash table.
  Each
  .Ar name
  is searched as if it were a command name and added to the hash table if it is
  an executable command.
  .Pp
  .It Xo
  .Ic jobs
  .Op Fl lnp
  .Op Ar job ...
  .Xc
  Display information about the specified job(s); if no jobs are specified, all
  jobs are displayed.
  The
  .Fl n
  option causes information to be displayed only for jobs that have changed
  state since the last notification.
  If the
  .Fl l
  option is used, the process ID of each process in a job is also listed.
  The
  .Fl p
  option causes only the process group of each job to be printed.
  See
  .Sx Job control
  below for the format of
  .Ar job
  and the displayed job.
  .Pp
  .It Xo
  .Ic kill
  .Oo Fl s Ar signame |
  .No - Ns Ar signum |
  .No - Ns Ar signame Oc
  .No { Ar job | pid | pgrp No }
  .Ar ...
  .Xc
  Send the specified signal to the specified jobs, process IDs, or process
  groups.
  If no signal is specified, the
  .Dv TERM
  signal is sent.
  If a job is specified, the signal is sent to the job's process group.
  See
  .Sx Job control
  below for the format of
  .Ar job .
  .Pp
  .It Xo
  .Ic kill
  .Fl l
  .Op Ar exit-status ...
  .Xc
  Print the signal name corresponding to
  .Ar exit-status .
  If no arguments are specified, a list of all the signals, their numbers, and
  a short description of them are printed.
  .Pp
  .It Ic let Op Ar expression ...
  Each expression is evaluated (see
  .Sx Arithmetic expressions
  above).
  If all expressions are successfully evaluated, the exit status is 0 (1)
  if the last expression evaluated to non-zero (zero).
  If an error occurs during
  the parsing or evaluation of an expression, the exit status is greater than 1.
  Since expressions may need to be quoted,
  .No (( Ar expr No ))
  is syntactic sugar for
  .No let \&" Ns Ar expr Ns \&" .
  .Pp
  .It Xo
  .Ic print
  .Oo
  .Fl nprsu Ns Oo Ar n Oc |
  .Fl R Op Fl en
  .Oc
  .Op Ar argument ...
  .Xc
  .Ic print
  prints its arguments on the standard output, separated by spaces and
  terminated with a newline.
  The
  .Fl n
  option suppresses the newline.
  By default, certain C escapes are translated.
  These include
  .Ql \eb ,
  .Ql \ef ,
  .Ql \en ,
  .Ql \er ,
  .Ql \et ,
  .Ql \ev ,
  and
  .Ql \e0###
  .Po
  .Ql #
  is an octal digit, of which there may be 0 to 3
  .Pc .
  .Ql \ec
  is equivalent to using the
  .Fl n
  option.
  .Ql \e
  expansion may be inhibited with the
  .Fl r
  option.
  The
  .Fl s
  option prints to the history file instead of standard output; the
  .Fl u
  option prints to file descriptor
  .Ar n
  .Po
  .Ar n
  defaults to 1 if omitted
  .Pc ;
  and the
  .Fl p
  option prints to the co-process (see
  .Sx Co-processes
  above).
  .Pp
  The
  .Fl R
  option is used to emulate, to some degree, the
  .Bx
  .Xr echo 1
  command, which does not process
  .Ql \e
  sequences unless the
  .Fl e
  option is given.
  As above, the
  .Fl n
  option suppresses the trailing newline.
  .Pp
  .It Ic pwd Op Fl LP
  Print the present working directory.
  If the
  .Fl L
  option is used or if the
  .Ic physical
  option isn't set (see the
  .Ic set
  command below), the logical path is printed (i.e. the path used to
  .Ic cd
  to the current directory).
  If the
  .Fl P
  option (physical path) is used or if the
  .Ic physical
  option is set, the path determined from the filesystem (by following
  .Sq ..
  directories to the root directory) is printed.
  .Pp
  .It Xo
  .Ic read
  .Op Fl prsu Ns Op Ar n
  .Op Ar parameter ...
  .Xc
  Reads a line of input from the standard input, separates the line into fields
  using the
  .Ev IFS
  parameter (see
  .Sx Substitution
  above), and assigns each field to the specified parameters.
  If there are more parameters than fields, the extra parameters are set to
  .Dv NULL ,
  or alternatively, if there are more fields than parameters, the last parameter
  is assigned the remaining fields (inclusive of any separating spaces).
  If no parameters are specified, the
  .Ev REPLY
  parameter is used.
  If the input line ends in a backslash and the
  .Fl r
  option was not used, the backslash and the newline are stripped and more input
  is read.
  If no input is read,
  .Ic read
  exits with a non-zero status.
  .Pp
  The first parameter may have a question mark and a string appended to it, in
  which case the string is used as a prompt (printed to standard error before
  any input is read) if the input is a
  .Xr tty 4
  (e.g.\&
  .Ic read nfoo?'number of foos: ' ) .
  .Pp
  The
  .Fl u Ns Ar n
  and
  .Fl p
  options cause input to be read from file descriptor
  .Ar n
  .Pf ( Ar n
  defaults to 0 if omitted)
  or the current co-process (see
  .Sx Co-processes
  above for comments on this), respectively.
  If the
  .Fl s
  option is used, input is saved to the history file.
  .Pp
  .It Xo
  .Ic readonly
  .Op Fl p
  .Oo Ar parameter
  .Op Ns = Ns Ar value
  .Ar ... Oc
  .Xc
  Sets the read-only attribute of the named parameters.
  If values are given,
  parameters are set to them before setting the attribute.
  Once a parameter is
  made read-only, it cannot be unset and its value cannot be changed.
  .Pp
  If no parameters are specified, the names of all parameters with the read-only
  attribute are printed one per line, unless the
  .Fl p
  option is used, in which case
  .Ic readonly
  commands defining all read-only parameters, including their values, are
  printed.
  .Pp
  .It Ic return Op Ar status
  Returns from a function or
  .Ic .\&
  script, with exit status
  .Ar status .
  If no
  .Ar status
  is given, the exit status of the last executed command is used.
  If used outside of a function or
  .Ic .\&
  script, it has the same effect as
  .Ic exit .
  Note that
  .Nm ksh
  treats both profile and
  .Ev ENV
  files as
  .Ic .\&
  scripts, while the original Korn shell only treats profiles as
  .Ic .\&
  scripts.
  .Pp
  .It Xo
  .Ic set Op Ic +-abCefhkmnpsuvXx
  .Op Ic +-o Ar option
  .Op Ic +-A Ar name
  .Op Fl -
  .Op Ar arg ...
  .Xc
  The
  .Ic set
  command can be used to set
  .Pq Ic -
  or clear
  .Pq Ic +
  shell options, set the positional parameters, or set an array parameter.
  Options can be changed using the
  .Cm +-o Ar option
  syntax, where
  .Ar option
  is the long name of an option, or using the
  .Cm +- Ns Ar letter
  syntax, where
  .Ar letter
  is the option's single letter name (not all options have a single letter name).
  The following table lists both option letters (if they exist) and long names
  along with a description of what the option does:
  .Bl -tag -width 15n
  .It Fl A Ar name
  Sets the elements of the array parameter
  .Ar name
  to
  .Ar arg ...
  If
  .Fl A
  is used, the array is reset (i.e. emptied) first; if
  .Ic +A
  is used, the first N elements are set (where N is the number of arguments);
  the rest are left untouched.
  .It Fl a | Ic allexport
  All new parameters are created with the export attribute.
  .It Fl b | Ic notify
  Print job notification messages asynchronously, instead of just before the
  prompt.
  Only used if job control is enabled
  .Pq Fl m .
  .It Fl C | Ic noclobber
  Prevent
  .Cm >
  redirection from overwriting existing files.
  Instead,
  .Cm >|
  must be used to force an overwrite.
  .It Fl e | Ic errexit
  Exit (after executing the
  .Dv ERR
  trap) as soon as an error occurs or a command fails (i.e. exits with a
  non-zero status).
  This does not apply to commands whose exit status is
  explicitly tested by a shell construct such as
  .Ic if ,
  .Ic until ,
  .Ic while ,
  or
  .Ic !\&
  statements.
  For
  .Ic &&
  or
  .Ic || ,
  only the status of the last command is tested.
  .It Fl f | Ic noglob
  Do not expand file name patterns.
  .It Fl h | Ic trackall
  Create tracked aliases for all executed commands (see
  .Sx Aliases
  above).
  Enabled by default for non-interactive shells.
  .It Fl k | Ic keyword
  Parameter assignments are recognized anywhere in a command.
  .It Fl m | Ic monitor
  Enable job control (default for interactive shells).
  .It Fl n | Ic noexec
  Do not execute any commands.
  Useful for checking the syntax of scripts
  (ignored if interactive).
  .It Fl p | Ic privileged
  The shell is a privileged shell.
  It is set automatically if, when the shell starts,
  the real UID or GID does not match
  the effective UID (EUID) or GID (EGID), respectively.
  See above for a description of what this means.
  .It Fl s | Ic stdin
  If used when the shell is invoked, commands are read from standard input.
  Set automatically if the shell is invoked with no arguments.
  .Pp
  When
  .Fl s
  is used with the
  .Ic set
  command it causes the specified arguments to be sorted before assigning them to
  the positional parameters (or to array
  .Ar name ,
  if
  .Fl A
  is used).
  .It Fl u | Ic nounset
  Referencing of an unset parameter is treated as an error, unless one of the
  .Ql - ,
  .Ql + ,
  or
  .Ql =
  modifiers is used.
  .It Fl v | Ic verbose
  Write shell input to standard error as it is read.
  .It Fl X | Ic markdirs
  Mark directories with a trailing
  .Ql /
  during file name generation.
  .It Fl x | Ic xtrace
  Print commands and parameter assignments when they are executed, preceded by
  the value of
  .Ev PS4 .
  .It Ic bgnice
  Background jobs are run with lower priority.
  .It Ic braceexpand
  Enable brace expansion (a.k.a. alternation).
  .It Ic csh-history
  Enables a subset of
  .Xr csh 1 Ns -style
  history editing using the
  .Ql !\&
  character.
  .It Ic emacs
  Enable BRL emacs-like command-line editing (interactive shells only); see
  .Sx Emacs editing mode .
  .It Ic gmacs
  Enable gmacs-like command-line editing (interactive shells only).
  Currently identical to emacs editing except that transpose (^T) acts slightly
  differently.
  .It Ic ignoreeof
  The shell will not (easily) exit when end-of-file is read;
  .Ic exit
  must be used.
  To avoid infinite loops, the shell will exit if
  .Dv EOF
  is read 13 times in a row.
  .It Ic interactive
  The shell is an interactive shell.
  This option can only be used when the shell is invoked.
  See above for a description of what this means.
  .It Ic login
  The shell is a login shell.
  This option can only be used when the shell is invoked.
  See above for a description of what this means.
  .It Ic nohup
  Do not kill running jobs with a
  .Dv SIGHUP
  signal when a login shell exits.
  Currently set by default;
  this is different from the original Korn shell (which
  doesn't have this option, but does send the
  .Dv SIGHUP
  signal).
  .It Ic nolog
  No effect.
  In the original Korn shell, this prevents function definitions from
  being stored in the history file.
  .It Ic physical
  Causes the
  .Ic cd
  and
  .Ic pwd
  commands to use
  .Dq physical
  (i.e. the filesystem's)
  .Sq ..
  directories instead of
  .Dq logical
  directories (i.e. the shell handles
  .Sq .. ,
  which allows the user to be oblivious of symbolic links to directories).
  Clear by default.
  Note that setting this option does not affect the current value of the
  .Ev PWD
  parameter; only the
  .Ic cd
  command changes
  .Ev PWD .
  See the
  .Ic cd
  and
  .Ic pwd
  commands above for more details.
  .It Ic posix
  Enable POSIX mode.
  See
  .Sx POSIX mode
  above.
  .It Ic restricted
  The shell is a restricted shell.
  This option can only be used when the shell is invoked.
  See above for a description of what this means.
  .It Ic sh
  Enable strict Bourne shell mode (see
  .Sx Strict Bourne shell mode
  above).
  .It Ic vi
  Enable
  .Xr vi 1 Ns -like
  command-line editing (interactive shells only).
  .It Ic vi-esccomplete
  In vi command-line editing, do command and file name completion when escape
  (^[) is entered in command mode.
  .It Ic vi-show8
  Prefix characters with the eighth bit set with
  .Sq M- .
  If this option is not set, characters in the range 128\-160 are printed as is,
  which may cause problems.
  .It Ic vi-tabcomplete
  In vi command-line editing, do command and file name completion when tab (^I)
  is entered in insert mode.
  This is the default.
  .It Ic viraw
  No effect.
  In the original Korn shell, unless
  .Ic viraw
  was set, the vi command-line mode would let the
  .Xr tty 4
  driver do the work until ESC (^[) was entered.
  .Nm ksh
  is always in viraw mode.
  .El
  .Pp
  These options can also be used upon invocation of the shell.
  The current set of
  options (with single letter names) can be found in the parameter
  .Sq $- .
  .Ic set Fl o
  with no option name will list all the options and whether each is on or off;
  .Ic set +o
  will print the current shell options in a form that
  can be reinput to the shell to achieve the same option settings.
  .Pp
  Remaining arguments, if any, are positional parameters and are assigned, in
  order, to the positional parameters (i.e. $1, $2, etc.).
  If options end with
  .Ql --
  and there are no remaining arguments, all positional parameters are cleared.
  If no options or arguments are given, the values of all names are printed.
  For unknown historical reasons, a lone
  .Ql -
  option is treated specially \- it clears both the
  .Fl x
  and
  .Fl v
  options.
  .Pp
  .It Ic shift Op Ar number
  The positional parameters
  .Ar number Ns +1 ,
  .Ar number Ns +2 ,
  etc. are renamed to
  .Sq 1 ,
  .Sq 2 ,
  etc.
  .Ar number
  defaults to 1.
  .Pp
  .It Ic suspend
  Stops the shell as if it had received the suspend character from
  the terminal.
  It is not possible to suspend a login shell unless the parent process
  is a member of the same terminal session but is a member of a different
  process group.
  As a general rule, if the shell was started by another shell or via
  .Xr su 1 ,
  it can be suspended.
  .Pp
  .It Ic test Ar expression
  .It Ic \&[ Ar expression Ic \&]
  .Ic test
  evaluates the
  .Ar expression
  and returns zero status if true, 1 if false, or greater than 1 if there
  was an error.
  It is normally used as the condition command of
  .Ic if
  and
  .Ic while
  statements.
  Symbolic links are followed for all
  .Ar file
  expressions except
  .Fl h
  and
  .Fl L .
  .Pp
  The following basic expressions are available:
  .Bl -tag -width 17n
  .It Fl a Ar file
  .Ar file
  exists.
  .It Fl b Ar file
  .Ar file
  is a block special device.
  .It Fl c Ar file
  .Ar file
  is a character special device.
  .It Fl d Ar file
  .Ar file
  is a directory.
  .It Fl e Ar file
  .Ar file
  exists.
  .It Fl f Ar file
  .Ar file
  is a regular file.
  .It Fl G Ar file
  .Ar file Ns 's
  group is the shell's effective group ID.
  .It Fl g Ar file
  .Ar file Ns 's
  mode has the setgid bit set.
  .It Fl h Ar file
  .Ar file
  is a symbolic link.
  .It Fl k Ar file
  .Ar file Ns 's
  mode has the
  .Xr sticky 8
  bit set.
  .It Fl L Ar file
  .Ar file
  is a symbolic link.
  .It Fl O Ar file
  .Ar file Ns 's
  owner is the shell's effective user ID.
  .It Fl o Ar option
  Shell
  .Ar option
  is set (see the
  .Ic set
  command above for a list of options).
  As a non-standard extension, if the option starts with a
  .Ql \&! ,
  the test is negated; the test always fails if
  .Ar option
  doesn't exist (so [ -o foo -o -o !foo ] returns true if and only if option
  .Ar foo
  exists).
  .It Fl p Ar file
  .Ar file
  is a named pipe.
  .It Fl r Ar file
  .Ar file
  exists and is readable.
  .It Fl S Ar file
  .Ar file
  is a
  .Xr unix 4 Ns -domain
  socket.
  .It Fl s Ar file
  .Ar file
  is not empty.
  .It Fl t Op Ar fd
  File descriptor
  .Ar fd
  is a
  .Xr tty 4
  device.
  If the
  .Ic posix
  option is not set,
  .Ar fd
  may be left out, in which case it is taken to be 1 (the behaviour differs due
  to the special POSIX rules described above).
  .It Fl u Ar file
  .Ar file Ns 's
  mode has the setuid bit set.
  .It Fl w Ar file
  .Ar file
  exists and is writable.
  .It Fl x Ar file
  .Ar file
  exists and is executable.
  .It Ar file1 Fl nt Ar file2
  .Ar file1
  is newer than
  .Ar file2
  or
  .Ar file1
  exists and
  .Ar file2
  does not.
  .It Ar file1 Fl ot Ar file2
  .Ar file1
  is older than
  .Ar file2
  or
  .Ar file2
  exists and
  .Ar file1
  does not.
  .It Ar file1 Fl ef Ar file2
  .Ar file1
  is the same file as
  .Ar file2 .
  .It Ar string
  .Ar string
  has non-zero length.
  .It Fl n Ar string
  .Ar string
  is not empty.
  .It Fl z Ar string
  .Ar string
  is empty.
  .It Ar string No = Ar string
  Strings are equal.
  .It Ar string No == Ar string
  Strings are equal.
  .It Ar string No != Ar string
  Strings are not equal.
  .It Ar string No > Ar string
  Strings compare greater than based on the ASCII value of their characters.
  .It Ar string No < Ar string
  Strings compare less than based on the ASCII value of their characters.
  .It Ar number Fl eq Ar number
  Numbers compare equal.
  .It Ar number Fl ne Ar number
  Numbers compare not equal.
  .It Ar number Fl ge Ar number
  Numbers compare greater than or equal.
  .It Ar number Fl gt Ar number
  Numbers compare greater than.
  .It Ar number Fl le Ar number
  Numbers compare less than or equal.
  .It Ar number Fl \&lt Ar number
  Numbers compare less than.
  .El
  .Pp
  The above basic expressions, in which unary operators have precedence over
  binary operators, may be combined with the following operators (listed in
  increasing order of precedence):
  .Bd -literal -offset indent
  expr -o expr		Logical OR.
  expr -a expr		Logical AND.
  ! expr			Logical NOT.
  ( expr )		Grouping.
  .Ed
  .Pp
  On operating systems not supporting
  .Pa /dev/fd/ Ns Ar n
  devices (where
  .Ar n
  is a file descriptor number), the
  .Ic test
  command will attempt to fake it for all tests that operate on files (except the
  .Fl e
  test).
  For example,
  [ -w /dev/fd/2 ] tests if file descriptor 2 is writable.
  .Pp
  Note that some special rules are applied (courtesy of POSIX)
  if the number of
  arguments to
  .Ic test
  or
  .Ic \&[ ... \&]
  is less than five: if leading
  .Ql \&!
  arguments can be stripped such that only one argument remains then a string
  length test is performed (again, even if the argument is a unary operator); if
  leading
  .Ql \&!
  arguments can be stripped such that three arguments remain and the second
  argument is a binary operator, then the binary operation is performed (even
  if the first argument is a unary operator, including an unstripped
  .Ql \&! ) .
  .Pp
  .Sy Note :
  A common mistake is to use
  .Dq if \&[ $foo = bar \&]
  which fails if parameter
  .Dq foo
  is
  .Dv NULL
  or unset, if it has embedded spaces (i.e.\&
  .Ev IFS
  characters), or if it is a unary operator like
  .Sq \&!
  or
  .Sq Fl n .
  Use tests like
  .Dq if \&[ \&"X$foo\&" = Xbar \&]
  instead.
  .Pp
  .It Xo
  .Ic time
  .Op Fl p
  .Op Ar pipeline
  .Xc
  If a
  .Ar pipeline
  is given, the times used to execute the pipeline are reported.
  If no pipeline
  is given, then the user and system time used by the shell itself, and all the
  commands it has run since it was started, are reported.
  The times reported are the real time (elapsed time from start to finish),
  the user CPU time (time spent running in user mode), and the system CPU time
  (time spent running in kernel mode).
  Times are reported to standard error; the format of the output is:
  .Pp
  .Dl "0m0.00s real     0m0.00s user     0m0.00s system"
  .Pp
  If the
  .Fl p
  option is given the output is slightly longer:
  .Bd -literal -offset indent
  real     0.00
  user     0.00
  sys      0.00
  .Ed
  .Pp
  It is an error to specify the
  .Fl p
  option unless
  .Ar pipeline
  is a simple command.
  .Pp
  Simple redirections of standard error do not affect the output of the
  .Ic time
  command:
  .Pp
  .Dl $ time sleep 1 2> afile
  .Dl $ { time sleep 1; } 2> afile
  .Pp
  Times for the first command do not go to
  .Dq afile ,
  but those of the second command do.
  .Pp
  .It Ic times
  Print the accumulated user and system times used both by the shell
  and by processes that the shell started which have exited.
  The format of the output is:
  .Bd -literal -offset indent
  0m0.00s 0m0.00s
  0m0.00s 0m0.00s
  .Ed
  .Pp
  .It Ic trap Op Ar handler signal ...
  Sets a trap handler that is to be executed when any of the specified signals are
  received.
  .Ar handler
  is either a
  .Dv NULL
  string, indicating the signals are to be ignored, a minus sign
  .Pq Sq - ,
  indicating that the default action is to be taken for the signals (see
  .Xr signal 3 ) ,
  or a string containing shell commands to be evaluated and executed at the first
  opportunity (i.e. when the current command completes, or before printing the
  next
  .Ev PS1
  prompt) after receipt of one of the signals.
  .Ar signal
  is the name of a signal (e.g.\&
  .Dv PIPE
  or
  .Dv ALRM )
  or the number of the signal (see the
  .Ic kill -l
  command above).
  .Pp
  There are two special signals:
  .Dv EXIT
  (also known as 0), which is executed when the shell is about to exit, and
  .Dv ERR ,
  which is executed after an error occurs (an error is something that would cause
  the shell to exit if the
  .Fl e
  or
  .Ic errexit
  option were set \- see the
  .Ic set
  command above).
  .Dv EXIT
  handlers are executed in the environment of the last executed command.
  Note
  that for non-interactive shells, the trap handler cannot be changed for signals
  that were ignored when the shell started.
  .Pp
  With no arguments,
  .Ic trap
  lists, as a series of
  .Ic trap
  commands, the current state of the traps that have been set since the shell
  started.
  Note that the output of
  .Ic trap
  cannot be usefully piped to another process (an artifact of the fact that
  traps are cleared when subprocesses are created).
  .Pp
  The original Korn shell's
  .Dv DEBUG
  trap and the handling of
  .Dv ERR
  and
  .Dv EXIT
  traps in functions are not yet implemented.
  .Pp
  .It Ic true
  A command that exits with a zero value.
  .Pp
  .It Ic type
  Short form of
  .Ic command Fl V
  (see above).
  .Pp
  .It Xo
  .Ic typeset
  .Oo
  .Op Ic +-lprtUux
  .Op Fl L Ns Op Ar n
  .Op Fl R Ns Op Ar n
  .Op Fl Z Ns Op Ar n
  .Op Fl i Ns Op Ar n
  .No \&| Fl f Op Fl tux
  .Oc
  .Oo
  .Ar name
  .Op Ns = Ns Ar value
  .Ar ...
  .Oc
  .Xc
  Display or set parameter attributes.
  With no
  .Ar name
  arguments, parameter attributes are displayed; if no options are used, the
  current attributes of all parameters are printed as
  .Ic typeset
  commands; if an option is given (or
  .Ql -
  with no option letter), all parameters and their values with the specified
  attributes are printed; if options are introduced with
  .Ql + ,
  parameter values are not printed.
  .Pp
  If
  .Ar name
  arguments are given, the attributes of the named parameters are set
  .Pq Ic -
  or cleared
  .Pq Ic + .
  Values for parameters may optionally be specified.
  If
  .Ic typeset
  is used inside a function, any newly created parameters are local to the
  function.
  .Pp
  When
  .Fl f
  is used,
  .Ic typeset
  operates on the attributes of functions.
  As with parameters, if no
  .Ar name
  arguments are given,
  functions are listed with their values (i.e. definitions) unless
  options are introduced with
  .Ql + ,
  in which case only the function names are reported.
  .Bl -tag -width Ds
  .It Fl f
  Function mode.
  Display or set functions and their attributes, instead of parameters.
  .It Fl i Ns Op Ar n
  Integer attribute.
  .Ar n
  specifies the base to use when displaying the integer (if not specified, the
  base given in the first assignment is used).
  Parameters with this attribute may
  be assigned values containing arithmetic expressions.
  .It Fl L Ns Op Ar n
  Left justify attribute.
  .Ar n
  specifies the field width.
  If
  .Ar n
  is not specified, the current width of a parameter (or the width of its first
  assigned value) is used.
  Leading whitespace (and zeros, if used with the
  .Fl Z
  option) is stripped.
  If necessary, values are either truncated or space padded
  to fit the field width.
  .It Fl l
  Lower case attribute.
  All upper case characters in values are converted to lower case.
  (In the original Korn shell, this parameter meant
  .Dq long integer
  when used with the
  .Fl i
  option.)
  .It Fl p
  Print complete
  .Ic typeset
  commands that can be used to re-create the attributes (but not the values) of
  parameters.
  This is the default action (option exists for ksh93 compatibility).
  .It Fl R Ns Op Ar n
  Right justify attribute.
  .Ar n
  specifies the field width.
  If
  .Ar n
  is not specified, the current width of a parameter (or the width of its first
  assigned value) is used.
  Trailing whitespace is stripped.
  If necessary, values are either stripped of leading characters or space
  padded to make them fit the field width.
  .It Fl r
  Read-only attribute.
  Parameters with this attribute may not be assigned to or unset.
  Once this attribute is set, it cannot be turned off.
  .It Fl t
  Tag attribute.
  Has no meaning to the shell; provided for application use.
  .Pp
  For functions,
  .Fl t
  is the trace attribute.
  When functions with the trace attribute are executed, the
  .Ic xtrace
  .Pq Fl x
  shell option is temporarily turned on.
  .It Fl U
  Unsigned integer attribute.
  Integers are printed as unsigned values (only
  useful when combined with the
  .Fl i
  option).
  This option is not in the original Korn shell.
  .It Fl u
  Upper case attribute.
  All lower case characters in values are converted to upper case.
  (In the original Korn shell, this parameter meant
  .Dq unsigned integer
  when used with the
  .Fl i
  option, which meant upper case letters would never be used for bases greater
  than 10.
  See the
  .Fl U
  option.)
  .Pp
  For functions,
  .Fl u
  is the undefined attribute.
  See
  .Sx Functions
  above for the implications of this.
  .It Fl x
  Export attribute.
  Parameters (or functions) are placed in the environment of
  any executed commands.
  Exported functions are not yet implemented.
  .It Fl Z Ns Op Ar n
  Zero fill attribute.
  If not combined with
  .Fl L ,
  this is the same as
  .Fl R ,
  except zero padding is used instead of space padding.
  .El
  .Pp
  .It Xo
  .Ic ulimit
  .Op Fl acdfHlmnpSst Op Ar value
  .Ar ...
  .Xc
  Display or set process limits.
  If no options are used, the file size limit
  .Pq Fl f
  is assumed.
  .Ar value ,
  if specified, may be either an arithmetic expression starting with a
  number or the word
  .Dq unlimited .
  The limits affect the shell and any processes created by the shell after a
  limit is imposed; limits may not be increased once they are set.
  .Bl -tag -width 5n
  .It Fl a
  Display all limits; unless
  .Fl H
  is used, soft limits are displayed.
  .It Fl c Ar n
  Impose a size limit of
  .Ar n
  blocks on the size of core dumps.
  .It Fl d Ar n
  Impose a size limit of
  .Ar n
  kilobytes on the size of the data area.
  .It Fl f Ar n
  Impose a size limit of
  .Ar n
  blocks on files written by the shell and its child processes (files of any
  size may be read).
  .It Fl H
  Set the hard limit only (the default is to set both hard and soft limits).
  .It Fl l Ar n
  Impose a limit of
  .Ar n
  kilobytes on the amount of locked (wired) physical memory.
  .It Fl m Ar n
  Impose a limit of
  .Ar n
  kilobytes on the amount of physical memory used.
  This limit is not enforced.
  .It Fl n Ar n
  Impose a limit of
  .Ar n
  file descriptors that can be open at once.
  .It Fl p Ar n
  Impose a limit of
  .Ar n
  processes that can be run by the user at any one time.
  .It Fl S
  Set the soft limit only (the default is to set both hard and soft limits).
  .It Fl s Ar n
  Impose a size limit of
  .Ar n
  kilobytes on the size of the stack area.
  .It Fl t Ar n
  Impose a time limit of
  .Ar n
  CPU seconds spent in user mode to be used by each process.
  .\".It Fl v Ar n
  .\"Impose a limit of
  .\"Ar n
  .\"kilobytes on the amount of virtual memory used.
  .El
  .Pp
  As far as
  .Ic ulimit
  is concerned, a block is 512 bytes.
  .Pp
  .It Xo
  .Ic umask
  .Op Fl S
  .Op Ar mask
  .Xc
  Display or set the file permission creation mask, or umask (see
  .Xr umask 2 ) .
  If the
  .Fl S
  option is used, the mask displayed or set is symbolic; otherwise, it is an
  octal number.
  .Pp
  Symbolic masks are like those used by
  .Xr chmod 1 .
  When used, they describe what permissions may be made available (as opposed to
  octal masks in which a set bit means the corresponding bit is to be cleared).
  For example,
  .Dq ug=rwx,o=
  sets the mask so files will not be readable, writable, or executable by
  .Dq others ,
  and is equivalent (on most systems) to the octal mask
  .Dq 007 .
  .Pp
  .It Xo
  .Ic unalias
  .Op Fl adt
  .Op Ar name ...
  .Xc
  The aliases for the given names are removed.
  If the
  .Fl a
  option is used, all aliases are removed.
  If the
  .Fl t
  or
  .Fl d
  options are used, the indicated operations are carried out on tracked or
  directory aliases, respectively.
  .Pp
  .It Xo
  .Ic unset
  .Op Fl fv
  .Ar parameter ...
  .Xc
  Unset the named parameters
  .Po
  .Fl v ,
  the default
  .Pc
  or functions
  .Pq Fl f .
  The exit status is non-zero if any of the parameters have the read-only
  attribute set, zero otherwise.
  .Pp
  .It Ic wait Op Ar job ...
  Wait for the specified job(s) to finish.
  The exit status of
  .Ic wait
  is that of the last specified job; if the last job is killed by a signal, the
  exit status is 128 + the number of the signal (see
  .Ic kill -l Ar exit-status
  above); if the last specified job can't be found (because it never existed, or
  had already finished), the exit status of
  .Ic wait
  is 127.
  See
  .Sx Job control
  below for the format of
  .Ar job .
  .Ic wait
  will return if a signal for which a trap has been set is received, or if a
  .Dv SIGHUP ,
  .Dv SIGINT ,
  or
  .Dv SIGQUIT
  signal is received.
  .Pp
  If no jobs are specified,
  .Ic wait
  waits for all currently running jobs (if any) to finish and exits with a zero
  status.
  If job monitoring is enabled, the completion status of jobs is printed
  (this is not the case when jobs are explicitly specified).
  .Pp
  .It Xo
  .Ic whence
  .Op Fl pv
  .Op Ar name ...
  .Xc
  For each
  .Ar name ,
  the type of command is listed (reserved word, built-in, alias,
  function, tracked alias, or executable).
  If the
  .Fl p
  option is used, a path search is performed even if
  .Ar name
  is a reserved word, alias, etc.
  Without the
  .Fl v
  option,
  .Ic whence
  is similar to
  .Ic command Fl v
  except that
  .Ic whence
  won't print aliases as alias commands.
  With the
  .Fl v
  option,
  .Ic whence
  is the same as
  .Ic command Fl V .
  Note that for
  .Ic whence ,
  the
  .Fl p
  option does not affect the search path used, as it does for
  .Ic command .
  If the type of one or more of the names could not be determined, the exit
  status is non-zero.
  .El
  .Ss Job control
  Job control refers to the shell's ability to monitor and control jobs, which
  are processes or groups of processes created for commands or pipelines.
  At a minimum, the shell keeps track of the status of the background (i.e.\&
  asynchronous) jobs that currently exist; this information can be displayed
  using the
  .Ic jobs
  commands.
  If job control is fully enabled (using
  .Ic set -m
  or
  .Ic set -o monitor ) ,
  as it is for interactive shells, the processes of a job are placed in their
  own process group.
  Foreground jobs can be stopped by typing the suspend
  character from the terminal (normally ^Z), jobs can be restarted in either the
  foreground or background using the
  .Ic fg
  and
  .Ic bg
  commands, and the state of the terminal is saved or restored when a foreground
  job is stopped or restarted, respectively.
  .Pp
  Note that only commands that create processes (e.g. asynchronous commands,
  subshell commands, and non-built-in, non-function commands) can be stopped;
  commands like
  .Ic read
  cannot be.
  .Pp
  When a job is created, it is assigned a job number.
  For interactive shells, this number is printed inside
  .Dq [..] ,
  followed by the process IDs of the processes in the job when an asynchronous
  command is run.
  A job may be referred to in the
  .Ic bg ,
  .Ic fg ,
  .Ic jobs ,
  .Ic kill ,
  and
  .Ic wait
  commands either by the process ID of the last process in the command pipeline
  (as stored in the
  .Ic $!\&
  parameter) or by prefixing the job number with a percent
  sign
  .Pq Sq % .
  Other percent sequences can also be used to refer to jobs:
  .Bl -tag -width "%+ | %% | %XX"
  .It %+ | %% | %
  The most recently stopped job or, if there are no stopped jobs, the oldest
  running job.
  .It %-
  The job that would be the
  .Ic %+
  job if the latter did not exist.
  .It % Ns Ar n
  The job with job number
  .Ar n .
  .It %? Ns Ar string
  The job with its command containing the string
  .Ar string
  (an error occurs if multiple jobs are matched).
  .It % Ns Ar string
  The job with its command starting with the string
  .Ar string
  (an error occurs if multiple jobs are matched).
  .El
  .Pp
  When a job changes state (e.g. a background job finishes or foreground job is
  stopped), the shell prints the following status information:
  .Pp
  .D1 [ Ns Ar number ] Ar flag status command
  .Pp
  where...
  .Bl -tag -width "command"
  .It Ar number
  is the job number of the job;
  .It Ar flag
  is the
  .Ql +
  or
  .Ql -
  character if the job is the
  .Ic %+
  or
  .Ic %-
  job, respectively, or space if it is neither;
  .It Ar status
  indicates the current state of the job and can be:
  .Bl -tag -width "RunningXX"
  .It Done Op Ar number
  The job exited.
  .Ar number
  is the exit status of the job, which is omitted if the status is zero.
  .It Running
  The job has neither stopped nor exited (note that running does not necessarily
  mean consuming CPU time \-
  the process could be blocked waiting for some event).
  .It Stopped Op Ar signal
  The job was stopped by the indicated
  .Ar signal
  (if no signal is given, the job was stopped by
  .Dv SIGTSTP ) .
  .It Ar signal-description Op Dq core dumped
  The job was killed by a signal (e.g. memory fault, hangup); use
  .Ic kill -l
  for a list of signal descriptions.
  The
  .Dq core dumped
  message indicates the process created a core file.
  .El
  .It Ar command
  is the command that created the process.
  If there are multiple processes in
  the job, each process will have a line showing its
  .Ar command
  and possibly its
  .Ar status ,
  if it is different from the status of the previous process.
  .El
  .Pp
  When an attempt is made to exit the shell while there are jobs in the stopped
  state, the shell warns the user that there are stopped jobs and does not exit.
  If another attempt is immediately made to exit the shell, the stopped jobs are
  sent a
  .Dv SIGHUP
  signal and the shell exits.
  Similarly, if the
  .Ic nohup
  option is not set and there are running jobs when an attempt is made to exit
  a login shell, the shell warns the user and does not exit.
  If another attempt
  is immediately made to exit the shell, the running jobs are sent a
  .Dv SIGHUP
  signal and the shell exits.
  .Ss Interactive input line editing
  The shell supports three modes of reading command lines from a
  .Xr tty 4
  in an interactive session, controlled by the
  .Ic emacs ,
  .Ic gmacs ,
  and
  .Ic vi
  options (at most one of these can be set at once).
  The default is
  .Ic emacs .
  Editing modes can be set explicitly using the
  .Ic set
  built-in, or implicitly via the
  .Ev EDITOR
  and
  .Ev VISUAL
  environment variables.
  If none of these options are enabled,
  the shell simply reads lines using the normal
  .Xr tty 4
  driver.
  If the
  .Ic emacs
  or
  .Ic gmacs
  option is set, the shell allows emacs-like editing of the command; similarly,
  if the
  .Ic vi
  option is set, the shell allows vi-like editing of the command.
  These modes are described in detail in the following sections.
  .Pp
  In these editing modes, if a line is longer than the screen width (see the
  .Ev COLUMNS
  parameter),
  a
  .Ql > ,
  .Ql + ,
  or
  .Ql <
  character is displayed in the last column indicating that there are more
  characters after, before and after, or before the current position,
  respectively.
  The line is scrolled horizontally as necessary.
  .Ss Emacs editing mode
  When the
  .Ic emacs
  option is set, interactive input line editing is enabled.
  Warning: This mode is
  slightly different from the emacs mode in the original Korn shell.
  In this mode, various editing commands
  (typically bound to one or more control characters) cause immediate actions
  without waiting for a newline.
  Several editing commands are bound to particular
  control characters when the shell is invoked; these bindings can be changed
  using the
  .Ic bind
  command.
  .Pp
  The following is a list of available editing commands.
  Each description starts with the name of the command,
  suffixed with a colon;
  an
  .Op Ar n
  (if the command can be prefixed with a count); and any keys the command is
  bound to by default, written using caret notation
  e.g. the ASCII ESC character is written as ^[.
  ^[A-Z] sequences are not case sensitive.
  A count prefix for a command is entered using the sequence
  .Pf ^[ Ar n ,
  where
  .Ar n
  is a sequence of 1 or more digits.
  Unless otherwise specified, if a count is
  omitted, it defaults to 1.
  .Pp
  Note that editing command names are used only with the
  .Ic bind
  command.
  Furthermore, many editing commands are useful only on terminals with
  a visible cursor.
  The default bindings were chosen to resemble corresponding
  Emacs key bindings.
  The user's
  .Xr tty 4
  characters (e.g.\&
  .Dv ERASE )
  are bound to
  reasonable substitutes and override the default bindings.
  .Bl -tag -width Ds
  .It abort: ^C, ^G
  Useful as a response to a request for a
  .Ic search-history
  pattern in order to abort the search.
  .It auto-insert: Op Ar n
  Simply causes the character to appear as literal input.
  Most ordinary characters are bound to this.
  .It Xo backward-char:
  .Op Ar n
  .No ^B , ^X^D
  .Xc
  Moves the cursor backward
  .Ar n
  characters.
  .It Xo backward-word:
  .Op Ar n
  .No ^[b
  .Xc
  Moves the cursor backward to the beginning of the word; words consist of
  alphanumerics, underscore
  .Pq Sq _ ,
  and dollar sign
  .Pq Sq $
  characters.
  .It beginning-of-history: ^[<
  Moves to the beginning of the history.
  .It beginning-of-line: ^A
  Moves the cursor to the beginning of the edited input line.
  .It Xo capitalize-word:
  .Op Ar n
  .No ^[C , ^[c
  .Xc
  Uppercase the first character in the next
  .Ar n
  words, leaving the cursor past the end of the last word.
  .It clear-screen: ^L
  Clears the screen if the
  .Ev TERM
  parameter is set and the terminal supports clearing the screen, then
  reprints the prompt string and the current input line.
  .It comment: ^[#
  If the current line does not begin with a comment character, one is added at
  the beginning of the line and the line is entered (as if return had been
  pressed); otherwise, the existing comment characters are removed and the cursor
  is placed at the beginning of the line.
  .It complete: ^[^[
  Automatically completes as much as is unique of the command name or the file
  name containing the cursor.
  If the entire remaining command or file name is
  unique, a space is printed after its completion, unless it is a directory name
  in which case
  .Ql /
  is appended.
  If there is no command or file name with the current partial word
  as its prefix, a bell character is output (usually causing a beep to be
  sounded).
  .Pp
  Custom completions may be configured by creating an array named
  .Ql complete_command ,
  optionally suffixed with an argument number to complete only for a single
  argument.
  So defining an array named
  .Ql complete_kill
  provides possible completions for any argument to the
  .Xr kill 1
  command, but
  .Ql complete_kill_1
  only completes the first argument.
  For example, the following command makes
  .Nm
  offer a selection of signal names for the first argument to
  .Xr kill 1 :
  .Pp
  .Dl set -A complete_kill_1 -- -9 -HUP -INFO -KILL -TERM
  .It complete-command: ^X^[
  Automatically completes as much as is unique of the command name having the
  partial word up to the cursor as its prefix, as in the
  .Ic complete
  command above.
  .It complete-file: ^[^X
  Automatically completes as much as is unique of the file name having the
  partial word up to the cursor as its prefix, as in the
  .Ic complete
  command described above.
  .It complete-list: ^I, ^[=
  Complete as much as is possible of the current word,
  and list the possible completions for it.
  If only one completion is possible,
  match as in the
  .Ic complete
  command above.
  .It Xo delete-char-backward:
  .Op Ar n
  .No ERASE , ^? , ^H
  .Xc
  Deletes
  .Ar n
  characters before the cursor.
  .It Xo delete-char-forward:
  .Op Ar n
  .No Delete
  .Xc
  Deletes
  .Ar n
  characters after the cursor.
  .It Xo delete-word-backward:
  .Op Ar n
  .No WERASE , ^[ERASE , ^W, ^[^? , ^[^H , ^[h
  .Xc
  Deletes
  .Ar n
  words before the cursor.
  .It Xo delete-word-forward:
  .Op Ar n
  .No ^[d
  .Xc
  Deletes
  .Ar n
  words after the cursor.
  .It Xo down-history:
  .Op Ar n
  .No ^N , ^XB
  .Xc
  Scrolls the history buffer forward
  .Ar n
  lines (later).
  Each input line originally starts just after the last entry
  in the history buffer, so
  .Ic down-history
  is not useful until either
  .Ic search-history
  or
  .Ic up-history
  has been performed.
  .It Xo downcase-word:
  .Op Ar n
  .No ^[L , ^[l
  .Xc
  Lowercases the next
  .Ar n
  words.
  .It end-of-history: ^[>
  Moves to the end of the history.
  .It end-of-line: ^E
  Moves the cursor to the end of the input line.
  .It eot: ^_
  Acts as an end-of-file; this is useful because edit-mode input disables
  normal terminal input canonicalization.
  .It Xo eot-or-delete:
  .Op Ar n
  .No ^D
  .Xc
  Acts as
  .Ic eot
  if alone on a line; otherwise acts as
  .Ic delete-char-forward .
  .It error:
  Error (ring the bell).
  .It exchange-point-and-mark: ^X^X
  Places the cursor where the mark is and sets the mark to where the cursor was.
  .It expand-file: ^[*
  Appends a
  .Ql *
  to the current word and replaces the word with the result of performing file
  globbing on the word.
  If no files match the pattern, the bell is rung.
  .It Xo forward-char:
  .Op Ar n
  .No ^F , ^XC
  .Xc
  Moves the cursor forward
  .Ar n
  characters.
  .It Xo forward-word:
  .Op Ar n
  .No ^[f
  .Xc
  Moves the cursor forward to the end of the
  .Ar n Ns th
  word.
  .It Xo goto-history:
  .Op Ar n
  .No ^[g
  .Xc
  Goes to history number
  .Ar n .
  .It kill-line: KILL
  Deletes the entire input line.
  .It Xo kill-to-eol:
  .Op Ar n
  .No ^K
  .Xc
  Deletes the input from the cursor to the end of the line if
  .Ar n
  is not specified; otherwise deletes characters between the cursor and column
  .Ar n .
  .It list: ^[?
  Prints a sorted, columnated list of command names or file names (if any) that
  can complete the partial word containing the cursor.
  Directory names have
  .Ql /
  appended to them.
  .It list-command: ^X?
  Prints a sorted, columnated list of command names (if any) that can complete
  the partial word containing the cursor.
  .It list-file: ^X^Y
  Prints a sorted, columnated list of file names (if any) that can complete the
  partial word containing the cursor.
  File type indicators are appended as described under
  .Ic list
  above.
  .It newline: ^J , ^M
  Causes the current input line to be processed by the shell.
  The current cursor position may be anywhere on the line.
  .It newline-and-next: ^O
  Causes the current input line to be processed by the shell, and the next line
  from history becomes the current line.
  This is only useful after an
  .Ic up-history
  or
  .Ic search-history .
  .It no-op: QUIT
  This does nothing.
  .It Xo prev-hist-word:
  .Op Ar n
  .No ^[. , ^[_
  .Xc
  The last
  .Pq Ar n Ns th
  word of the previous command is inserted at the cursor.
  .It quote: ^^
  The following character is taken literally rather than as an editing command.
  .It redraw:
  Reprints the prompt string and the current input line.
  .It Xo search-character-backward:
  .Op Ar n
  .No ^[^]
  .Xc
  Search backward in the current line for the
  .Ar n Ns th
  occurrence of the next character typed.
  .It Xo search-character-forward:
  .Op Ar n
  .No ^]
  .Xc
  Search forward in the current line for the
  .Ar n Ns th
  occurrence of the next character typed.
  .It search-history: ^R
  Enter incremental search mode.
  The internal history list is searched
  backwards for commands matching the input.
  An initial
  .Ql ^
  in the search string anchors the search.
  The abort key will leave search mode.
  Other commands will be executed after leaving search mode.
  Successive
  .Ic search-history
  commands continue searching backward to the next previous occurrence of the
  pattern.
  The history buffer retains only a finite number of lines; the oldest
  are discarded as necessary.
  .It set-mark-command: ^[ Ns Aq space
  Set the mark at the cursor position.
  .It transpose-chars: ^T
  If at the end of line, or if the
  .Ic gmacs
  option is set, this exchanges the two previous characters; otherwise, it
  exchanges the previous and current characters and moves the cursor one
  character to the right.
  .It Xo up-history:
  .Op Ar n
  .No ^P , ^XA
  .Xc
  Scrolls the history buffer backward
  .Ar n
  lines (earlier).
  .It Xo upcase-word:
  .Op Ar n
  .No ^[U , ^[u
  .Xc
  Uppercase the next
  .Ar n
  words.
  .It quote: ^V
  Synonym for ^^.
  .It yank: ^Y
  Inserts the most recently killed text string at the current cursor position.
  .It yank-pop: ^[y
  Immediately after a
  .Ic yank ,
  replaces the inserted text string with the next previously killed text string.
  .El
  .Pp
  The following editing commands lack default bindings but can be used with the
  .Ic bind
  command:
  .Bl -tag -width Ds
  .It kill-region
  Deletes the input between the cursor and the mark.
  .El
  .Ss Vi editing mode
  The vi command-line editor in
  .Nm
  has basically the same commands as the
  .Xr vi 1
  editor with the following exceptions:
  .Bl -bullet
  .It
  You start out in insert mode.
  .It
  There are file name and command completion commands:
  =, \e, *, ^X, ^E, ^F, and, optionally,
  .Aq tab
  and
  .Aq esc .
  .It
  The
  .Ic _
  command is different (in
  .Nm
  it is the last argument command; in
  .Xr vi 1
  it goes to the start of the current line).
  .It
  The
  .Ic /
  and
  .Ic G
  commands move in the opposite direction to the
  .Ic j
  command.
  .It
  Commands which don't make sense in a single line editor are not available
  (e.g. screen movement commands and
  .Xr ex 1 Ns -style
  colon
  .Pq Ic \&:
  commands).
  .El
  .Pp
  Note that the ^X stands for control-X; also
  .Aq esc ,
  .Aq space ,
  and
  .Aq tab
  are used for escape, space, and tab, respectively (no kidding).
  .Pp
  Like
  .Xr vi 1 ,
  there are two modes:
  .Dq insert
  mode and
  .Dq command
  mode.
  In insert mode, most characters are simply put in the buffer at the
  current cursor position as they are typed; however, some characters are
  treated specially.
  In particular, the following characters are taken from current
  .Xr tty 4
  settings
  (see
  .Xr stty 1 )
  and have their usual meaning (normal values are in parentheses): kill (^U),
  erase (^?), werase (^W), eof (^D), intr (^C), and quit (^\e).
  In addition to
  the above, the following characters are also treated specially in insert mode:
  .Bl -tag -width 10n
  .It ^E
  Command and file name enumeration (see below).
  .It ^F
  Command and file name completion (see below).
  If used twice in a row, the
  list of possible completions is displayed; if used a third time, the completion
  is undone.
  .It ^H
  Erases previous character.
  .It ^J | ^M
  End of line.
  The current line is read, parsed, and executed by the shell.
  .It ^V
  Literal next.
  The next character typed is not treated specially (can be used
  to insert the characters being described here).
  .It ^X
  Command and file name expansion (see below).
  .It Aq esc
  Puts the editor in command mode (see below).
  .It Aq tab
  Optional file name and command completion (see
  .Ic ^F
  above), enabled with
  .Ic set -o vi-tabcomplete .
  .El
  .Pp
  In command mode, each character is interpreted as a command.
  Characters that
  don't correspond to commands, are illegal combinations of commands, or are
  commands that can't be carried out, all cause beeps.
  In the following command descriptions, an
  .Op Ar n
  indicates the command may be prefixed by a number (e.g.\&
  .Ic 10l
  moves right 10 characters); if no number prefix is used,
  .Ar n
  is assumed to be 1 unless otherwise specified.
  The term
  .Dq current position
  refers to the position between the cursor and the character preceding the
  cursor.
  A
  .Dq word
  is a sequence of letters, digits, and underscore characters or a sequence of
  non-letter, non-digit, non-underscore, and non-whitespace characters (e.g.\&
  .Dq ab2*&^
  contains two words) and a
  .Dq big-word
  is a sequence of non-whitespace characters.
  .Pp
  Special
  .Nm
  vi commands:
  .Pp
  The following commands are not in, or are different from, the normal vi file
  editor:
  .Bl -tag -width 10n
  .It Xo
  .Oo Ar n Oc Ns _
  .Xc
  Insert a space followed by the
  .Ar n Ns th
  big-word from the last command in the history at the current position and enter
  insert mode; if
  .Ar n
  is not specified, the last word is inserted.
  .It #
  Insert the comment character
  .Pq Sq #
  at the start of the current line and return the line to the shell (equivalent
  to
  .Ic I#^J ) .
  .It Xo
  .Oo Ar n Oc Ns g
  .Xc
  Like
  .Ic G ,
  except if
  .Ar n
  is not specified, it goes to the most recent remembered line.
  .It Xo
  .Oo Ar n Oc Ns v
  .Xc
  Edit line
  .Ar n
  using the
  .Xr vi 1
  editor; if
  .Ar n
  is not specified, the current line is edited.
  The actual command executed is
  .Ic fc -e ${VISUAL:-${EDITOR:-vi}} Ar n .
  .It * and ^X
  Command or file name expansion is applied to the current big-word (with an
  appended
  .Ql *
  if the word contains no file globbing characters) \- the big-word is replaced
  with the resulting words.
  If the current big-word is the first on the line
  or follows one of the characters
  .Ql \&; ,
  .Ql | ,
  .Ql & ,
  .Ql \&( ,
  or
  .Ql \&) ,
  and does not contain a slash
  .Pq Sq / ,
  then command expansion is done; otherwise file name expansion is done.
  Command expansion will match the big-word against all aliases, functions, and
  built-in commands as well as any executable files found by searching the
  directories in the
  .Ev PATH
  parameter.
  File name expansion matches the big-word against the files in the
  current directory.
  After expansion, the cursor is placed just past the last
  word and the editor is in insert mode.
  .It Xo
  .Oo Ar n Oc Ns \e ,
  .Oo Ar n Oc Ns ^F ,
  .Oo Ar n Oc Ns Aq tab ,
  .No and
  .Oo Ar n Oc Ns Aq esc
  .Xc
  Command/file name completion.
  Replace the current big-word with the
  longest unique match obtained after performing command and file name expansion.
  .Aq tab
  is only recognized if the
  .Ic vi-tabcomplete
  option is set, while
  .Aq esc
  is only recognized if the
  .Ic vi-esccomplete
  option is set (see
  .Ic set -o ) .
  If
  .Ar n
  is specified, the
  .Ar n Ns th
  possible completion is selected (as reported by the command/file name
  enumeration command).
  .It = and ^E
  Command/file name enumeration.
  List all the commands or files that match the current big-word.
  .It @ Ns Ar c
  Macro expansion.
  Execute the commands found in the alias
  .No _ Ns Ar c .
  .El
  .Pp
  Intra-line movement commands:
  .Bl -tag -width Ds
  .It Xo
  .Oo Ar n Oc Ns h and
  .Oo Ar n Oc Ns ^H
  .Xc
  Move left
  .Ar n
  characters.
  .It Xo
  .Oo Ar n Oc Ns l and
  .Oo Ar n Oc Ns Aq space
  .Xc
  Move right
  .Ar n
  characters.
  .It 0
  Move to column 0.
  .It ^
  Move to the first non-whitespace character.
  .It Xo
  .Oo Ar n Oc Ns |
  .Xc
  Move to column
  .Ar n .
  .It $
  Move to the last character.
  .It Xo
  .Oo Ar n Oc Ns b
  .Xc
  Move back
  .Ar n
  words.
  .It Xo
  .Oo Ar n Oc Ns B
  .Xc
  Move back
  .Ar n
  big-words.
  .It Xo
  .Oo Ar n Oc Ns e
  .Xc
  Move forward to the end of the word,
  .Ar n
  times.
  .It Xo
  .Oo Ar n Oc Ns E
  .Xc
  Move forward to the end of the big-word,
  .Ar n
  times.
  .It Xo
  .Oo Ar n Oc Ns w
  .Xc
  Move forward
  .Ar n
  words.
  .It Xo
  .Oo Ar n Oc Ns W
  .Xc
  Move forward
  .Ar n
  big-words.
  .It %
  Find match.
  The editor looks forward for the nearest parenthesis, bracket, or
  brace and then moves the cursor to the matching parenthesis, bracket, or brace.
  .It Xo
  .Oo Ar n Oc Ns f Ns Ar c
  .Xc
  Move forward to the
  .Ar n Ns th
  occurrence of the character
  .Ar c .
  .It Xo
  .Oo Ar n Oc Ns F Ns Ar c
  .Xc
  Move backward to the
  .Ar n Ns th
  occurrence of the character
  .Ar c .
  .It Xo
  .Oo Ar n Oc Ns t Ns Ar c
  .Xc
  Move forward to just before the
  .Ar n Ns th
  occurrence of the character
  .Ar c .
  .It Xo
  .Oo Ar n Oc Ns T Ns Ar c
  .Xc
  Move backward to just before the
  .Ar n Ns th
  occurrence of the character
  .Ar c .
  .It Xo
  .Oo Ar n Oc Ns \&;
  .Xc
  Repeats the last
  .Ic f , F , t ,
  or
  .Ic T
  command.
  .It Xo
  .Oo Ar n Oc Ns \&,
  .Xc
  Repeats the last
  .Ic f , F , t ,
  or
  .Ic T
  command, but moves in the opposite direction.
  .El
  .Pp
  Inter-line movement commands:
  .Bl -tag -width Ds
  .It Xo
  .Oo Ar n Oc Ns j ,
  .Oo Ar n Oc Ns + ,
  .No and
  .Oo Ar n Oc Ns ^N
  .Xc
  Move to the
  .Ar n Ns th
  next line in the history.
  .It Xo
  .Oo Ar n Oc Ns k ,
  .Oo Ar n Oc Ns - ,
  .No and
  .Oo Ar n Oc Ns ^P
  .Xc
  Move to the
  .Ar n Ns th
  previous line in the history.
  .It Xo
  .Oo Ar n Oc Ns G
  .Xc
  Move to line
  .Ar n
  in the history; if
  .Ar n
  is not specified, the number of the first remembered line is used.
  .It Xo
  .Oo Ar n Oc Ns g
  .Xc
  Like
  .Ic G ,
  except if
  .Ar n
  is not specified, it goes to the most recent remembered line.
  .It Xo
  .Oo Ar n Oc Ns / Ns Ar string
  .Xc
  Search backward through the history for the
  .Ar n Ns th
  line containing
  .Ar string ;
  if
  .Ar string
  starts with
  .Ql ^ ,
  the remainder of the string must appear at the start of the history line for
  it to match.
  .It Xo
  .Oo Ar n Oc Ns \&? Ns Ar string
  .Xc
  Same as
  .Ic / ,
  except it searches forward through the history.
  .It Xo
  .Oo Ar n Oc Ns n
  .Xc
  Search for the
  .Ar n Ns th
  occurrence of the last search string;
  the direction of the search is the same as the last search.
  .It Xo
  .Oo Ar n Oc Ns N
  .Xc
  Search for the
  .Ar n Ns th
  occurrence of the last search string;
  the direction of the search is the opposite of the last search.
  .El
  .Pp
  Edit commands
  .Bl -tag -width Ds
  .It Xo
  .Oo Ar n Oc Ns a
  .Xc
  Append text
  .Ar n
  times; goes into insert mode just after the current position.
  The append is
  only replicated if command mode is re-entered i.e.\&
  .Aq esc
  is used.
  .It Xo
  .Oo Ar n Oc Ns A
  .Xc
  Same as
  .Ic a ,
  except it appends at the end of the line.
  .It Xo
  .Oo Ar n Oc Ns i
  .Xc
  Insert text
  .Ar n
  times; goes into insert mode at the current position.
  The insertion is only
  replicated if command mode is re-entered i.e.\&
  .Aq esc
  is used.
  .It Xo
  .Oo Ar n Oc Ns I
  .Xc
  Same as
  .Ic i ,
  except the insertion is done just before the first non-blank character.
  .It Xo
  .Oo Ar n Oc Ns s
  .Xc
  Substitute the next
  .Ar n
  characters (i.e. delete the characters and go into insert mode).
  .It S
  Substitute whole line.
  All characters from the first non-blank character to the
  end of the line are deleted and insert mode is entered.
  .It Xo
  .Oo Ar n Oc Ns c Ns Ar move-cmd
  .Xc
  Change from the current position to the position resulting from
  .Ar n move-cmd Ns s
  (i.e. delete the indicated region and go into insert mode); if
  .Ar move-cmd
  is
  .Ic c ,
  the line starting from the first non-blank character is changed.
  .It C
  Change from the current position to the end of the line (i.e. delete to the
  end of the line and go into insert mode).
  .It Xo
  .Oo Ar n Oc Ns x
  .Xc
  Delete the next
  .Ar n
  characters.
  .It Xo
  .Oo Ar n Oc Ns X
  .Xc
  Delete the previous
  .Ar n
  characters.
  .It D
  Delete to the end of the line.
  .It Xo
  .Oo Ar n Oc Ns d Ns Ar move-cmd
  .Xc
  Delete from the current position to the position resulting from
  .Ar n move-cmd Ns s ;
  .Ar move-cmd
  is a movement command (see above) or
  .Ic d ,
  in which case the current line is deleted.
  .It Xo
  .Oo Ar n Oc Ns r Ns Ar c
  .Xc
  Replace the next
  .Ar n
  characters with the character
  .Ar c .
  .It Xo
  .Oo Ar n Oc Ns R
  .Xc
  Replace.
  Enter insert mode but overwrite existing characters instead of
  inserting before existing characters.
  The replacement is repeated
  .Ar n
  times.
  .It Xo
  .Oo Ar n Oc Ns ~
  .Xc
  Change the case of the next
  .Ar n
  characters.
  .It Xo
  .Oo Ar n Oc Ns y Ns Ar move-cmd
  .Xc
  Yank from the current position to the position resulting from
  .Ar n move-cmd Ns s
  into the yank buffer; if
  .Ar move-cmd
  is
  .Ic y ,
  the whole line is yanked.
  .It Y
  Yank from the current position to the end of the line.
  .It Xo
  .Oo Ar n Oc Ns p
  .Xc
  Paste the contents of the yank buffer just after the current position,
  .Ar n
  times.
  .It Xo
  .Oo Ar n Oc Ns P
  .Xc
  Same as
  .Ic p ,
  except the buffer is pasted at the current position.
  .El
  .Pp
  Miscellaneous vi commands
  .Bl -tag -width Ds
  .It ^J and ^M
  The current line is read, parsed, and executed by the shell.
  .It ^L and ^R
  Redraw the current line.
  .It Xo
  .Oo Ar n Oc Ns \&.
  .Xc
  Redo the last edit command
  .Ar n
  times.
  .It u
  Undo the last edit command.
  .It U
  Undo all changes that have been made to the current line.
  .It Ar intr No and Ar quit
  The interrupt and quit terminal characters cause the current line to be
  deleted and a new prompt to be printed.
  .El
  .Sh FILES
  .Bl -tag -width "/etc/suid_profileXX" -compact
  .It Pa ~/.profile
  User's login profile.
  .It Pa /etc/ksh.kshrc
  Global configuration file.
  Not sourced by default.
  .It Pa /etc/profile
  System login profile.
  .It Pa /etc/shells
  Shell database.
  .It Pa /etc/suid_profile
  Privileged shell profile.
  .El
  .Sh SEE ALSO
  .Xr csh 1 ,
  .Xr ed 1 ,
  .Xr mg 1 ,
  .Xr sh 1 ,
  .Xr stty 1 ,
  .Xr vi 1 ,
  .Xr shells 5 ,
  .Xr environ 7 ,
  .Xr script 7
  .Rs
  .%A Morris Bolsky
  .%A David Korn
  .%B The KornShell Command and Programming Language
  .%D First Edition 1989
  .%I Prentice Hall
  .%O ISBN 0135169720
  .\" The second edition of the above book (1995) is about ksh93,
  .\" but the OpenBSD ksh is a descendant from ksh88 via pdksh.
  .Re
  .Rs
  .%A Stephen G. Kochan
  .%A Patrick H. Wood
  .%B UNIX Shell Programming, 3rd Edition
  .%D 2003
  .%I Sams
  .%O ISBN 0672324903
  .Re
  .Rs
  .%A IEEE Inc.
  .%D 1993
  .%O ISBN 1-55937-266-9
  .%T IEEE Standard for Information Technology \- Portable Operating \
      System Interface (POSIX) \- Part 2: Shell and Utilities
  .Re
  .Sh VERSION
  This page documents version @(#)PD KSH v5.2.14 99/07/13.2 of the public
  domain Korn shell.
  .Sh AUTHORS
  .An -nosplit
  This shell is based on the public domain 7th edition Bourne shell clone by
  .An Charles Forsyth
  and parts of the BRL shell by
  .An Doug A. Gwyn ,
  .An Doug Kingston ,
  .An Ron Natalie ,
  .An Arnold Robbins ,
  .An Lou Salkind ,
  and others.
  The first release of
  .Nm pdksh
  was created by
  .An Eric Gisin ,
  and it was subsequently maintained by
  .An John R. MacMillan Aq Mt change!john@sq.sq.com ,
  .An Simon J. Gerraty Aq Mt sjg@zen.void.oz.au ,
  and
  .An Michael Rendell Aq Mt michael@cs.mun.ca .
  The
  .Pa CONTRIBUTORS
  file in the source distribution contains a more complete list of people and
  their part in the shell's development.
  .Sh BUGS
  .Pf $( Ar command )
  expressions are currently parsed by finding the closest matching (unquoted)
  parenthesis.
  Thus constructs inside
  .Pf $( Ar command )
  may produce an error.
  For example, the parenthesis in
  .Ql x);;
  is interpreted as the closing parenthesis in
  .Ql $(case x in x);; *);; esac) .