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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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putenv(3) Library Functions Manual putenv(3)
putenv - change or add an environment variable
Standard C library (libc, -lc)
#include <stdlib.h>
int putenv(char *string);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
putenv():
_XOPEN_SOURCE
|| /* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE
The putenv() function adds or changes the value of environment
variables. The argument string is of the form name=value. If
name does not already exist in the environment, then string is
added to the environment. If name does exist, then the value of
name in the environment is changed to value. The string pointed
to by string becomes part of the environment, so altering the
string changes the environment.
The putenv() function returns zero on success. On failure, it
returns a nonzero value, and errno is set to indicate the error.
ENOMEM Insufficient space to allocate new environment.
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────┬───────────────┬─────────────────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────┼───────────────┼─────────────────────┤
│ putenv() │ Thread safety │ MT-Unsafe const:env │
└─────────────────────────┴───────────────┴─────────────────────┘
POSIX.1-2008.
POSIX.1-2001, SVr2, 4.3BSD-Reno.
The putenv() function is not required to be reentrant, and the
one in glibc 2.0 is not, but the glibc 2.1 version is.
Since glibc 2.1.2, the glibc implementation conforms to SUSv2:
the pointer string given to putenv() is used. In particular,
this string becomes part of the environment; changing it later
will change the environment. (Thus, it is an error to call
putenv() with an automatic variable as the argument, then return
from the calling function while string is still part of the
environment.) However, from glibc 2.0 to glibc 2.1.1, it
differs: a copy of the string is used. On the one hand this
causes a memory leak, and on the other hand it violates SUSv2.
The 4.3BSD-Reno version, like glibc 2.0, uses a copy; this is
fixed in all modern BSDs.
SUSv2 removes the const from the prototype, and so does glibc
2.1.3.
The GNU C library implementation provides a nonstandard
extension. If string does not include an equal sign:
putenv("NAME");
then the named variable is removed from the caller's environment.
clearenv(3), getenv(3), setenv(3), unsetenv(3), environ(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.9.1 2024-05-02 putenv(3)
Pages that refer to this page: clearenv(3), getenv(3), pam_putenv(3), setenv(3), proc_pid_environ(5), environ(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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