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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  26 .\" References consulted:
  27 .\"     Linux libc source code
  28 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  29 .\"     386BSD man pages
  30 .\" Modified Sat Jul 24 18:20:58 1993 by Rik Faith (faith@cs.unc.edu)
  31 .\" Modified Fri Feb 14 21:47:50 1997 by Andries Brouwer (aeb@cwi.nl)
  32 .\" Modified 9 Jun 2004, Michael Kerrisk <mtk.manpages@gmail.com>
  33 .\"     Changed unsetenv() prototype; added EINVAL error
  34 .\"     Noted nonstandard behavior of setenv() if name contains '='
  35 .\" 2005-08-12, mtk, glibc 2.3.4 fixed the "name contains '='" bug
  36 .\"
  37 .TH SETENV 3  2016-03-15 "GNU" "Linux Programmer's Manual"
  38 .SH NAME
  39 setenv \- change or add an environment variable
  40 .SH SYNOPSIS
  41 .nf
  42 .B #include <stdlib.h>
  43 .PP
  44 .BI "int setenv(const char *" name ", const char *" value ", int " overwrite );
  45 .PP
  46 .BI "int unsetenv(const char *" name );
  47 .fi
  48 .PP
  49 .in -4n
  50 Feature Test Macro Requirements for glibc (see
  51 .BR feature_test_macros (7)):
  52 .in
  53 .PP
  54 .ad l
  55 .BR setenv (),
  56 .BR unsetenv ():
  57 .RS 4
  58 _POSIX_C_SOURCE\ >=\ 200112L
  59     || /* Glibc versions <= 2.19: */ _BSD_SOURCE
  60 .RE
  61 .ad b
  62 .SH DESCRIPTION
  63 The
  64 .BR setenv ()
  65 function adds the variable
  66 .I name
  67 to the
  68 environment with the value
  69 .IR value ,
  70 if
  71 .I name
  72 does not
  73 already exist.
  74 If
  75 .I name
  76 does exist in the environment, then
  77 its value is changed to
  78 .IR value
  79 if
  80 .I overwrite
  81 is nonzero;
  82 if
  83 .IR overwrite
  84 is zero, then the value of
  85 .I name
  86 is not changed (and
  87 .BR setenv ()
  88 returns a success status).
  89 This function makes copies of the strings pointed to by
  90 .I name
  91 and
  92 .I value
  93 (by contrast with
  94 .BR putenv (3)).
  95 .PP
  96 The
  97 .BR unsetenv ()
  98 function deletes the variable
  99 .I name
 100 from
 101 the environment.
 102 If
 103 .I name
 104 does not exist in the environment,
 105 then the function succeeds, and the environment is unchanged.
 106 .SH RETURN VALUE
 107 The
 108 .BR setenv ()
 109 function returns zero on success,
 110 or \-1 on error, with
 111 .I errno
 112 set to indicate the cause of the error.
 113
 114 The
 115 .BR unsetenv ()
 116 function returns zero on success,
 117 or \-1 on error, with
 118 .I errno
 119 set to indicate the cause of the error.
 120 .SH ERRORS
 121 .TP
 122 .B EINVAL
 123 .I name
 124 is NULL, points to a string of length 0,
 125 or contains an \(aq=\(aq character.
 126 .TP
 127 .B ENOMEM
 128 Insufficient memory to add a new variable to the environment.
 129 .SH ATTRIBUTES
 130 For an explanation of the terms used in this section, see
 131 .BR attributes (7).
 132 .ad l
 133 .TS
 134 allbox;
 135 lb lb lb
 136 l l l.
 137 Interface       Attribute       Value
 138 T{
 139 .BR setenv (),
 140 .BR unsetenv ()
 141 T}      Thread safety   MT-Unsafe const:env
 142 .TE
 143 .ad
 144 .SH CONFORMING TO
 145 POSIX.1-2001, POSIX.1-2008, 4.3BSD.
 146 .SH NOTES
 147 POSIX.1 does not require
 148 .BR setenv ()
 149 or
 150 .BR unsetenv ()
 151 to be reentrant.
 152
 153 Prior to glibc 2.2.2,
 154 .BR unsetenv ()
 155 was prototyped
 156 as returning
 157 .IR void ;
 158 more recent glibc versions follow the
 159 POSIX.1-compliant prototype shown in the SYNOPSIS.
 160 .SH BUGS
 161 POSIX.1 specifies that if
 162 .I name
 163 contains an \(aq=\(aq character, then
 164 .BR setenv ()
 165 should fail with the error
 166 .BR EINVAL ;
 167 however, versions of glibc before 2.3.4 allowed an \(aq=\(aq sign in
 168 .IR name .
 169 .SH SEE ALSO
 170 .BR clearenv (3),
 171 .BR getenv (3),
 172 .BR putenv (3),
 173 .BR environ (7)