man3/setenv.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
   2 .\" and Copyright (C) 2004, 2007 Michael kerrisk <mtk.manpages@gmail.com>
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  13 .\" Since the Linux kernel and libraries are constantly changing, this
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  24 .\" References consulted:
  25 .\"     Linux libc source code
  26 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  27 .\"     386BSD man pages
  28 .\" Modified Sat Jul 24 18:20:58 1993 by Rik Faith (faith@cs.unc.edu)
  29 .\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl)
  30 .\" Modified 9 Jun 2004, Michael Kerrisk <mtk.manpages@gmail.com>
  31 .\"     Changed unsetenv() prototype; added EINVAL error
  32 .\"     Noted non-standard behavior of setenv() if name contains '='
  33 .\" 2005-08-12, mtk, glibc 2.3.4 fixed the "name contains '='" bug
  34 .\"
  35 .TH SETENV 3  2007-07-26 "GNU" "Linux Programmer's Manual"
  36 .SH NAME
  37 setenv \- change or add an environment variable
  38 .SH SYNOPSIS
  39 .nf
  40 .B #include <stdlib.h>
  41 .sp
  42 .BI "int setenv(const char *" name ", const char *" value ", int " overwrite );
  43 .sp
  44 .BI "int unsetenv(const char *" name );
  45 .fi
  46 .sp
  47 .in -4n
  48 Feature Test Macro Requirements for glibc (see
  49 .BR feature_test_macros (7)):
  50 .in
  51 .sp
  52 .ad l
  53 .BR setenv (),
  54 .BR unsetenv ():
  55 _BSD_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600
  56 .ad b
  57 .SH DESCRIPTION
  58 The
  59 .BR setenv ()
  60 function adds the variable \fIname\fP to the
  61 environment with the value \fIvalue\fP, if \fIname\fP does not
  62 already exist.
  63 If \fIname\fP does exist in the environment, then
  64 its value is changed to \fIvalue\fP if \fIoverwrite\fP is non-zero;
  65 if \fIoverwrite\fP is zero, then the value of \fIname\fP is not
  66 changed.
  67 This function makes copies of the strings pointed to by
  68 .I name
  69 and
  70 .I value
  71 (by contrast with
  72 .BR putenv (3)).
  73 .PP
  74 The
  75 .BR unsetenv ()
  76 function deletes the variable \fIname\fP from
  77 the environment.
  78 If
  79 .I name
  80 does not exist in the environment,
  81 then the function succeeds, and the environment is unchanged.
  82 .SH "RETURN VALUE"
  83 The
  84 .BR setenv ()
  85 function returns zero on success, or \-1 if there
  86 was insufficient space in the environment.
  87
  88 The
  89 .BR unsetenv ()
  90 function returns zero on success,
  91 or \-1 on error, with
  92 .I errno
  93 set to indicate the cause of the error.
  94 .SH "ERRORS"
  95 .TP
  96 .B EINVAL
  97 .I name
  98 contained an \'=\' character.
  99 .SH "CONFORMING TO"
 100 4.3BSD, POSIX.1-2001.
 101 .SH "NOTES"
 102 POSIX.1-2001 does not require
 103 .BR setenv ()
 104 or
 105 .BR unsetenv ()
 106 to be reentrant.
 107
 108 Prior to glibc 2.2.2,
 109 .BR unsetenv ()
 110 was prototyped
 111 as returning \fIvoid\fP; more recent glibc versions follow the
 112 POSIX.1-2001-compliant prototype shown in the SYNOPSIS.
 113 .SH BUGS
 114 POSIX.1-2001 specifies that if
 115 .I name
 116 contains an \'=\' character, then
 117 .BR setenv ()
 118 should fail with the error
 119 .BR EINVAL ;
 120 however, versions of glibc before 2.3.4 allowed an \'=\' sign in
 121 .IR name .
 122 .SH "SEE ALSO"
 123 .BR clearenv (3),
 124 .BR getenv (3),
 125 .BR putenv (3),
 126 .BR environ (7)