setenv(3) — Linux manual page

NAME \| LIBRARY \| SYNOPSIS \| DESCRIPTION \| RETURN VALUE \| ERRORS \| ATTRIBUTES \| STANDARDS \| HISTORY \| CAVEATS \| BUGS \| SEE ALSO

setenv(3)               Library Functions Manual               setenv(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, int overwrite);
       int unsetenv(const char *name);

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       setenv(), unsetenv():
           _POSIX_C_SOURCE >= 200112L
               || /* glibc <= 2.19: */ _BSD_SOURCE

DESCRIPTION top

       The setenv() function adds the variable name to the environment
       with the value value, if name does not already exist.  If name
       does exist in the environment, then its value is changed to value
       if overwrite is nonzero; if overwrite is zero, then the value of
       name is not changed (and setenv() returns a success status).
       This function makes copies of the strings pointed to by name and
       value (by contrast with putenv(3)).

       The unsetenv() function deletes the variable name from the
       environment.  If name does not exist in the environment, then the
       function succeeds, and the environment is unchanged.

RETURN VALUE top

       setenv() and unsetenv() functions return zero on success, or -1
       on error, with errno set to indicate the error.

ERRORS top

       EINVAL name is NULL, points to a string of length 0, or contains
              an '=' character.

       ENOMEM Insufficient memory to add a new variable to the
              environment.

ATTRIBUTES top

       For an explanation of the terms used in this section, see
       attributes(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 returning
       void; more recent glibc versions follow the POSIX.1-compliant
       prototype shown in the SYNOPSIS.

CAVEATS top

       POSIX.1 does not require setenv() or unsetenv() to be reentrant.

BUGS top

       POSIX.1 specifies that if name contains an '=' character, then
       setenv() should fail with the error EINVAL; however, versions of
       glibc before glibc 2.3.4 allowed an '=' sign in name.

SEE ALSO top

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

Linux man-pages 6.04           2023-03-30                      setenv(3)