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  2017-09-15 "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 .BR setenv ()
 108 and
 109 .BR unsetenv ()
 110 functions return zero on success,
 111 or \-1 on error, with
 112 .I errno
 113 set to indicate the cause of the error.
 114 .SH ERRORS
 115 .TP
 116 .B EINVAL
 117 .I name
 118 is NULL, points to a string of length 0,
 119 or contains an \(aq=\(aq character.
 120 .TP
 121 .B ENOMEM
 122 Insufficient memory to add a new variable to the environment.
 123 .SH ATTRIBUTES
 124 For an explanation of the terms used in this section, see
 125 .BR attributes (7).
 126 .ad l
 127 .TS
 128 allbox;
 129 lb lb lb
 130 l l l.
 131 Interface       Attribute       Value
 132 T{
 133 .BR setenv (),
 134 .BR unsetenv ()
 135 T}      Thread safety   MT-Unsafe const:env
 136 .TE
 137 .ad
 138 .SH CONFORMING TO
 139 POSIX.1-2001, POSIX.1-2008, 4.3BSD.
 140 .SH NOTES
 141 POSIX.1 does not require
 142 .BR setenv ()
 143 or
 144 .BR unsetenv ()
 145 to be reentrant.
 146 .PP
 147 Prior to glibc 2.2.2,
 148 .BR unsetenv ()
 149 was prototyped
 150 as returning
 151 .IR void ;
 152 more recent glibc versions follow the
 153 POSIX.1-compliant prototype shown in the SYNOPSIS.
 154 .SH BUGS
 155 POSIX.1 specifies that if
 156 .I name
 157 contains an \(aq=\(aq character, then
 158 .BR setenv ()
 159 should fail with the error
 160 .BR EINVAL ;
 161 however, versions of glibc before 2.3.4 allowed an \(aq=\(aq sign in
 162 .IR name .
 163 .SH SEE ALSO
 164 .BR clearenv (3),
 165 .BR getenv (3),
 166 .BR putenv (3),
 167 .BR environ (7)