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GETENV(3) Library Functions Manual GETENV(3)

getenv, putenv, setenv, unsetenv — environment variable functions

#include <stdlib.h>

char *
getenv(const char *name);

int
setenv(const char *name, const char *value, int overwrite);

int
putenv(const char *string);

void
unsetenv(const char *name);

These functions set, unset and fetch environment variables from the host . For compatibility with differing environment conventions, the given arguments name and value may be appended and prepended, respectively, with an equal sign “=”.

The () function obtains the current value of the environment variable, name. If the variable name is not in the current environment, a null pointer is returned.

The () function inserts or resets the environment variable name in the current environment list. If the variable name does not exist in the list, it is inserted with the given value. If the variable does exist, the argument overwrite is tested; if overwrite is zero, the variable is not reset, otherwise it is reset to the given value.

The () function takes an argument of the form ``name=value'' and is equivalent to:

setenv(name, value, 1);

The () function deletes all instances of the variable name pointed to by name from the list.

The functions setenv() and putenv() return zero if successful; otherwise the global variable errno is set to indicate the error and a -1 is returned.

[]
The function setenv() or putenv() failed because they were unable to allocate memory for the environment.

csh(1), sh(1), execve(2), environ(7)

The getenv() function conforms to ANSI X3.159-1989 (“ANSI C89”).

The functions setenv() and unsetenv() appeared in Version 7 AT&T UNIX. The putenv() function appeared in 4.3BSD-Reno.

4.4BSD-Lite2 December 11, 1993 GETENV(3)