IABSD.fr/src/bin/expr/expr.1

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• Author : schwarze
  Date : 2017-08-16 20:10:58
  Hash : 0b877f7b
  Message : Explicitly say that expr(1) handles decimal integers only, as mandated by POSIX and as implemented in our utility; triggered by a question from Alessandro DE LAURENZIS <just22 at atlantide dot t28 dot net> on misc@. OK millert@

• bin/expr/expr.1

• .\"	$OpenBSD: expr.1,v 1.24 2017/08/16 20:10:58 schwarze Exp $
  .\"	$NetBSD: expr.1,v 1.9 1995/04/28 23:27:13 jtc Exp $
  .\"
  .\" Written by J.T. Conklin <jtc@netbsd.org>.
  .\" Public domain.
  .\"
  .Dd $Mdocdate: August 16 2017 $
  .Dt EXPR 1
  .Os
  .Sh NAME
  .Nm expr
  .Nd evaluate expression
  .Sh SYNOPSIS
  .Nm expr
  .Ar expression
  .Sh DESCRIPTION
  The
  .Nm
  utility evaluates
  .Ar expression
  and writes the result on standard output.
  All operators are separate arguments to the
  .Nm
  utility.
  Characters special to the command interpreter must be escaped.
  .Pp
  Operators are listed below in order of increasing precedence.
  Operators with equal precedence are grouped within { } symbols.
  .Bl -tag -width indent
  .It Ar expr1 | expr2
  Returns the evaluation of
  .Ar expr1
  if it is neither an empty string nor zero;
  otherwise, returns the evaluation of
  .Ar expr2 .
  .It Ar expr1 Li & Ar expr2
  Returns the evaluation of
  .Ar expr1
  if neither expression evaluates to an empty string or zero;
  otherwise, returns zero.
  .It Ar expr1 Li "{=, >, >=, <, <=, !=}" Ar expr2
  Returns the results of integer comparison if both arguments are
  decimal integers; otherwise, returns the results of string comparison
  using the locale-specific collation sequence.
  The result of each comparison is 1 if the specified relation is true,
  or 0 if the relation is false.
  .It Ar expr1 Li "{+, -}" Ar expr2
  Returns the results of addition or subtraction of decimal integer-valued
  arguments.
  .It Ar expr1 Li "{*, /, %}" Ar expr2
  Returns the results of multiplication, integer division, or remainder of
  decimal integer-valued arguments.
  .It Ar expr1 Li \&: Ar expr2
  The
  .Ql \&:
  operator matches
  .Ar expr1
  against
  .Ar expr2 ,
  which must be a basic regular expression.
  The regular expression is anchored
  to the beginning of the string with an implicit
  .Ql ^ .
  .Pp
  If the match succeeds and the pattern contains at least one regular
  expression subexpression
  .Dq "\e(...\e)" ,
  the string corresponding to
  .Dq "\e1"
  is returned;
  otherwise, the matching operator returns the number of characters matched.
  If the match fails and the pattern contains a regular expression subexpression
  the null string is returned;
  otherwise, returns 0.
  .Pp
  Note: the empty string cannot be matched using
  .Bd -literal -offset indent
  expr '' : '$'
  .Ed
  .Pp
  This is because the returned number of matched characters
  .Pq zero
  is indistinguishable from a failed match, so
  .Nm
  returns failure
  .Pq 0 .
  To match the empty string, use a structure such as:
  .Bd -literal -offset indent
  expr X'' : 'X$'
  .Ed
  .El
  .Pp
  Parentheses are used for grouping in the usual manner.
  .Sh EXIT STATUS
  The
  .Nm
  utility exits with one of the following values:
  .Pp
  .Bl -tag -width Ds -offset indent -compact
  .It 0
  The expression is neither an empty string nor 0.
  .It 1
  The expression is an empty string or 0.
  .It 2
  The expression is invalid.
  .It \*(Gt2
  An error occurred (such as memory allocation failure).
  .El
  .Sh EXAMPLES
  Add 1 to the variable
  .Va a :
  .Bd -literal -offset indent
  $ a=`expr $a + 1`
  .Ed
  .Pp
  Return the filename portion of a pathname stored
  in variable
  .Va a .
  The
  .Ql //
  characters act to eliminate ambiguity with the division operator:
  .Bd -literal -offset indent
  $ expr "//$a" \&: '.*/\e(.*\e)'
  .Ed
  .Pp
  Return the number of characters in variable
  .Va a :
  .Bd -literal -offset indent
  $ expr $a \&: '.*'
  .Ed
  .Sh SEE ALSO
  .Xr test 1 ,
  .Xr re_format 7
  .Sh STANDARDS
  The
  .Nm
  utility is compliant with the
  .St -p1003.1-2008
  specification.
  .Sh HISTORY
  The
  .Nm
  utility first appeared in the Programmer's Workbench (PWB/UNIX)
  and has supported regular expressions since
  .At v7 .
  It was rewritten from scratch for
  .Bx 386 0.1
  and again for
  .Nx 1.1 .
  .Sh AUTHORS
  .An -nosplit
  The first free version was written by
  .An Pace Willisson
  in 1992.
  This version was written by
  .An John T. Conklin
  in 1994.