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SETENV(3) Linux Programmer's Manual SETENV(3) NAME setenv - change or add an environment variable SYNOPSIS #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 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 environβ ment is unchanged. RETURN VALUE setenv() and unsetenv() functions return zero on success, or -1 on error, with errno set to indicate the error. ERRORS 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 For an explanation of the terms used in this section, see attributes(7). ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ¬ββββββββββββββββ¬ββββββββββββββββββββββ βInterface β Attribute β Value β ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββΌββββββββββββββββΌββββββββββββββββββββββ€ βsetenv(), unsetenv() β Thread safety β MT-Unsafe const:env β ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββ΄ββββββββββββββββββββββ CONFORMING TO POSIX.1-2001, POSIX.1-2008, 4.3BSD. NOTES 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. BUGS 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. SEE ALSO clearenv(3), getenv(3), putenv(3), environ(7) GNU 2021-03-22 SETENV(3)