IABSD.fr/src/lib/libc/stdlib/getenv.3

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• Author : millert
  Date : 2022-08-08 22:40:03
  Hash : 7fd658f2
  Message : For putenv(3), return an error if string starts with a '=' character. Both FreeBSD and NetBSD have this behavior. OK deraadt@

• lib/libc/stdlib/getenv.3

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  .\"	$OpenBSD: getenv.3,v 1.23 2022/08/08 22:40:03 millert Exp $
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  .Dd $Mdocdate: August 8 2022 $
  .Dt GETENV 3
  .Os
  .Sh NAME
  .Nm getenv ,
  .Nm putenv ,
  .Nm setenv ,
  .Nm unsetenv
  .Nd environment variable functions
  .Sh SYNOPSIS
  .In stdlib.h
  .Ft char *
  .Fn getenv "const char *name"
  .Ft int
  .Fn setenv "const char *name" "const char *value" "int overwrite"
  .Ft int
  .Fn putenv "char *string"
  .Ft int
  .Fn unsetenv "const char *name"
  .Sh DESCRIPTION
  These functions set, unset, and fetch environment variables from the host
  .Em environment list .
  .Pp
  The
  .Fn getenv
  function obtains the current value of the environment variable
  .Fa name .
  If the variable
  .Fa name
  is not in the current environment, a null pointer is returned.
  .Pp
  The
  .Fn setenv
  function inserts or resets the environment variable
  .Fa name
  in the current environment list.
  If the variable
  .Fa name
  does not exist in the list, it is inserted with the given
  .Fa value .
  If the variable does exist, the argument
  .Fa overwrite
  is tested; if
  .Fa overwrite
  is zero, the variable is not reset, otherwise it is reset to the given
  .Fa value .
  .Pp
  The
  .Fn putenv
  function takes an argument of the form
  .Ar name Ns = Ns Ar value .
  The memory pointed to by
  .Ar string
  becomes part of the environment and must not be deallocated by the caller.
  If the variable already exists, it will be overwritten.
  A common source of bugs is to pass a
  .Ar string
  argument that is a locally scoped string buffer.
  This will result in corruption of the environment after leaving
  the scope in which the variable is defined.
  For this reason, the
  .Fn setenv
  function is preferred over
  .Fn putenv .
  .Pp
  The
  .Fn unsetenv
  function deletes all instances of the variable name pointed to by
  .Fa name
  from the list.
  .Sh RETURN VALUES
  .Rv -std putenv setenv unsetenv
  .Pp
  The
  .Fn getenv
  function returns a pointer to the requested value, or
  .Dv NULL
  if it could not be found.
  If
  .Fn getenv
  is successful, the string returned should be considered read-only.
  .Sh ERRORS
  .Bl -tag -width Er
  .It Bq Er EINVAL
  The
  .Fn setenv
  or
  .Fn unsetenv
  function was passed an empty
  .Ar name
  or a NULL pointer, or was passed a
  .Ar name
  containing an
  .Sq =
  character.
  .Pp
  The
  .Fn putenv
  function was passed a
  .Ar string
  that did not contain an
  .Sq =
  character, or was passed a
  .Ar string
  that started with the
  .Sq =
  character.
  .It Bq Er ENOMEM
  The
  .Fn setenv
  or
  .Fn putenv
  function failed because it was unable to allocate memory for the environment.
  .El
  .Sh SEE ALSO
  .Xr csh 1 ,
  .Xr sh 1 ,
  .Xr execve 2 ,
  .Xr issetugid 2 ,
  .Xr environ 7
  .Sh STANDARDS
  The
  .Fn getenv
  function conforms to
  .St -ansiC .
  The
  .Fn putenv ,
  .Fn setenv ,
  and
  .Fn unsetenv
  functions conform to
  .St -p1003.1-2008 .
  .Sh HISTORY
  The function
  .Fn getenv
  appeared in
  .At v7
  and
  .Bx 3 .
  The functions
  .Fn setenv
  and
  .Fn unsetenv
  appeared in
  .Bx 4.3 Tahoe .
  The
  .Fn putenv
  function first appeared in
  .At V.2
  and was reimplemented for
  .Bx 4.3 Reno .
  .Sh CAVEATS
  Library code must be careful about using
  .Fn getenv
  to read untrusted environment variables in setuid programs.
  The
  .Fn issetugid
  function is provided for this purpose.