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setenv(3) — Linux manual page

setenv(3)                Library Functions Manualsetenv(3)

NAME        top

       setenv - change or add an environment variable

LIBRARY        top

       Standard C library (libc,-lc)

SYNOPSIS        top

#include <stdlib.h>int setenv(const char *name, const char *value, intoverwrite);int unsetenv(const char *name);   Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):setenv(),unsetenv():           _POSIX_C_SOURCE >= 200112L               || /* glibc <= 2.19: */ _BSD_SOURCE

DESCRIPTION        top

       Thesetenv() function adds the variablename to the environment       with the valuevalue, ifname does not already exist.  Ifname       does exist in the environment, then its value is changed tovalue       ifoverwrite is nonzero; ifoverwrite is zero, then the value ofname is not changed (andsetenv() returns a success status).  This       function makes copies of the strings pointed to byname andvalue       (by contrast withputenv(3)).       Theunsetenv() function deletes the variablename from the       environment.  Ifname does not exist in the environment, then the       function succeeds, and the environment is unchanged.

RETURN VALUE        top

setenv() andunsetenv() functions return zero on success, or -1 on       error, witherrno set to indicate the error.

ERRORS        top

EINVALname is NULL, points to a string of length 0, or contains              an '=' character.ENOMEMInsufficient memory to add a new variable to the              environment.

ATTRIBUTES        top

       For an explanation of the terms used in this section, seeattributes(7).       ┌──────────────────────────┬───────────────┬─────────────────────┐       │Interface│Attribute│Value│       ├──────────────────────────┼───────────────┼─────────────────────┤       │setenv(),unsetenv()     │ Thread safety │ MT-Unsafe const:env │       └──────────────────────────┴───────────────┴─────────────────────┘

STANDARDS        top

       POSIX.1-2008.

HISTORY        top

       POSIX.1-2001, 4.3BSD.       Prior to glibc 2.2.2,unsetenv() was prototyped as returningvoid;       more recent glibc versions follow the POSIX.1-compliant prototype       shown in the SYNOPSIS.

CAVEATS        top

       POSIX.1 does not requiresetenv() orunsetenv() to be reentrant.

BUGS        top

       POSIX.1 specifies that ifname contains an '=' character, thensetenv() should fail with the errorEINVAL; however, versions of       glibc before glibc 2.3.4 allowed an '=' sign inname.

SEE ALSO        top

clearenv(3),getenv(3),putenv(3),environ(7)

COLOPHON        top

       This page is part of theman-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-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  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 isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17setenv(3)

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