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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  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  2009-09-20 "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,
  86 or \-1 on error, with
  87 .I errno
  88 set to indicate the cause of the error.
  89
  90 The
  91 .BR unsetenv ()
  92 function returns zero on success,
  93 or \-1 on error, with
  94 .I errno
  95 set to indicate the cause of the error.
  96 .SH "ERRORS"
  97 .TP
  98 .B EINVAL
  99 .I name
 100 is NULL, points to a string of length 0,
 101 or contains an \(aq=\(aq character.
 102 .TP
 103 .B ENOMEM
 104 Insufficient memory to add a new variable to the environment.
 105 .SH "CONFORMING TO"
 106 4.3BSD, POSIX.1-2001.
 107 .SH "NOTES"
 108 POSIX.1-2001 does not require
 109 .BR setenv ()
 110 or
 111 .BR unsetenv ()
 112 to be reentrant.
 113
 114 Prior to glibc 2.2.2,
 115 .BR unsetenv ()
 116 was prototyped
 117 as returning \fIvoid\fP; more recent glibc versions follow the
 118 POSIX.1-2001-compliant prototype shown in the SYNOPSIS.
 119 .SH BUGS
 120 POSIX.1-2001 specifies that if
 121 .I name
 122 contains an \(aq=\(aq character, then
 123 .BR setenv ()
 124 should fail with the error
 125 .BR EINVAL ;
 126 however, versions of glibc before 2.3.4 allowed an \(aq=\(aq sign in
 127 .IR name .
 128 .SH "SEE ALSO"
 129 .BR clearenv (3),
 130 .BR getenv (3),
 131 .BR putenv (3),
 132 .BR environ (7)