Manpages - setenv.3

setenv - change or add an environment variable

  #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

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.

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

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.

For an explanation of the terms used in this section, see *attributes*(7).

POSIX.1-2001, POSIX.1-2008, 4.3BSD.

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

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.

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

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

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