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  2009-09-20 "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 .sp
  44 .BI "int setenv(const char *" name ", const char *" value ", int " overwrite );
  45 .sp
  46 .BI "int unsetenv(const char *" name );
  47 .fi
  48 .sp
  49 .in -4n
  50 Feature Test Macro Requirements for glibc (see
  51 .BR feature_test_macros (7)):
  52 .in
  53 .sp
  54 .ad l
  55 .BR setenv (),
  56 .BR unsetenv ():
  57 .RS 4
  58 _BSD_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600
  59 .RE
  60 .ad b
  61 .SH DESCRIPTION
  62 The
  63 .BR setenv ()
  64 function adds the variable \fIname\fP to the
  65 environment with the value \fIvalue\fP, if \fIname\fP does not
  66 already exist.
  67 If \fIname\fP does exist in the environment, then
  68 its value is changed to \fIvalue\fP if \fIoverwrite\fP is nonzero;
  69 if \fIoverwrite\fP is zero, then the value of \fIname\fP is not
  70 changed.
  71 This function makes copies of the strings pointed to by
  72 .I name
  73 and
  74 .I value
  75 (by contrast with
  76 .BR putenv (3)).
  77 .PP
  78 The
  79 .BR unsetenv ()
  80 function deletes the variable \fIname\fP from
  81 the environment.
  82 If
  83 .I name
  84 does not exist in the environment,
  85 then the function succeeds, and the environment is unchanged.
  86 .SH RETURN VALUE
  87 The
  88 .BR setenv ()
  89 function returns zero on success,
  90 or \-1 on error, with
  91 .I errno
  92 set to indicate the cause of the error.
  93
  94 The
  95 .BR unsetenv ()
  96 function returns zero on success,
  97 or \-1 on error, with
  98 .I errno
  99 set to indicate the cause of the error.
 100 .SH ERRORS
 101 .TP
 102 .B EINVAL
 103 .I name
 104 is NULL, points to a string of length 0,
 105 or contains an \(aq=\(aq character.
 106 .TP
 107 .B ENOMEM
 108 Insufficient memory to add a new variable to the environment.
 109 .SH CONFORMING TO
 110 4.3BSD, POSIX.1-2001.
 111 .SH NOTES
 112 POSIX.1-2001 does not require
 113 .BR setenv ()
 114 or
 115 .BR unsetenv ()
 116 to be reentrant.
 117
 118 Prior to glibc 2.2.2,
 119 .BR unsetenv ()
 120 was prototyped
 121 as returning \fIvoid\fP; more recent glibc versions follow the
 122 POSIX.1-2001-compliant prototype shown in the SYNOPSIS.
 123 .SH BUGS
 124 POSIX.1-2001 specifies that if
 125 .I name
 126 contains an \(aq=\(aq character, then
 127 .BR setenv ()
 128 should fail with the error
 129 .BR EINVAL ;
 130 however, versions of glibc before 2.3.4 allowed an \(aq=\(aq sign in
 131 .IR name .
 132 .SH SEE ALSO
 133 .BR clearenv (3),
 134 .BR getenv (3),
 135 .BR putenv (3),
 136 .BR environ (7)