unsetenv - Man Page

remove an environment variable


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <stdlib.h>

int unsetenv(const char *name);


The unsetenv() function shall remove an environment variable from the environment of the calling process. The name argument points to a string, which is the name of the variable to be removed. The named argument shall not contain an '=' character. If the named variable does not exist in the current environment, the environment shall be unchanged and the function is considered to have completed successfully.

The unsetenv() function shall update the list of pointers to which environ points.

The unsetenv() function need not be thread-safe.

Return Value

Upon successful completion, zero shall be returned. Otherwise, -1 shall be returned, errno set to indicate the error, and the environment shall be unchanged.


The unsetenv() function shall fail if:


The name argument points to an empty string, or points to a string containing an '=' character.

The following sections are informative.



Application Usage



Refer to the RATIONALE section in setenv().

Future Directions


See Also

getenv(), setenv()

The Base Definitions volume of POSIX.1-2017, <stdlib.h>, <sys_types.h>

Referenced By

getenv(3p), setenv(3p), stdlib.h(0p).

2017 IEEE/The Open Group POSIX Programmer's Manual