1PUTENV(3)                  Linux Programmer's Manual                 PUTENV(3)
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NAME

6       putenv - change or add an environment variable
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SYNOPSIS

9       #include <stdlib.h>
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11       int putenv(char *string);
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13   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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15       putenv(): _XOPEN_SOURCE
16           || /* Glibc since 2.19: */ _DEFAULT_SOURCE
17           || /* Glibc versions <= 2.19: */ _SVID_SOURCE
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DESCRIPTION

20       The  putenv()  function  adds or changes the value of environment vari‐
21       ables.  The argument string is of the form name=value.   If  name  does
22       not already exist in the environment, then string is added to the envi‐
23       ronment.  If name does exist, then the value of name in the environment
24       is  changed  to value.  The string pointed to by string becomes part of
25       the environment, so altering the string changes the environment.
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RETURN VALUE

28       The putenv() function returns zero on success, or nonzero if  an  error
29       occurs.  In the event of an error, errno is set to indicate the cause.
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ERRORS

32       ENOMEM Insufficient space to allocate new environment.
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ATTRIBUTES

35       For   an   explanation   of   the  terms  used  in  this  section,  see
36       attributes(7).
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38       ┌──────────┬───────────────┬─────────────────────┐
39       │Interface │ Attribute     │ Value               │
40       ├──────────┼───────────────┼─────────────────────┤
41       │putenv()  │ Thread safety │ MT-Unsafe const:env │
42       └──────────┴───────────────┴─────────────────────┘

CONFORMING TO

44       POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
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NOTES

47       The putenv() function is not required to be reentrant, and the  one  in
48       glibc 2.0 is not, but the glibc 2.1 version is.
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50       Since  version  2.1.2,  the glibc implementation conforms to SUSv2: the
51       pointer string given to putenv() is used.  In particular,  this  string
52       becomes  part  of  the  environment;  changing it later will change the
53       environment.  (Thus, it is an error is to call putenv() with  an  auto‐
54       matic  variable  as the argument, then return from the calling function
55       while string is still part of the environment.)   However,  glibc  ver‐
56       sions  2.0  to  2.1.1 differ: a copy of the string is used.  On the one
57       hand this causes a memory leak, and  on  the  other  hand  it  violates
58       SUSv2.
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60       The 4.4BSD version, like glibc 2.0, uses a copy.
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62       SUSv2 removes the const from the prototype, and so does glibc 2.1.3.
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SEE ALSO

65       clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)
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COLOPHON

68       This  page  is  part of release 4.15 of the Linux man-pages project.  A
69       description of the project, information about reporting bugs,  and  the
70       latest     version     of     this    page,    can    be    found    at
71       https://www.kernel.org/doc/man-pages/.
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75GNU                               2016-03-15                         PUTENV(3)
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