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.
unsetenv — remove an environment variable
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.
Upon successful completion, zero shall be returned. Otherwise, -1 shall be
returned, errno set to indicate the error, and the environment shall be
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.
Refer to the RATIONALE section in setenv().
The Base Definitions volume of POSIX.1‐2017,
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1-2017, Standard for Information Technology -- Portable Operating
System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018
Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html .
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