unsetenvname

unsetenvname is a term used in programming and system administration to denote the name of an environment variable that is targeted by an unset operation. It is not a standard API name or command; rather, it serves as a generic identifier for the variable being removed from a process's environment.

In C and POSIX-compliant libraries, the actual operation is performed by the function unsetenv; the usual prototype is int unsetenv(const char *name). If successful, the environment variable named by name is removed from the process's environment; if the variable does not exist, some implementations return success while others set errno. The name should not be NULL or empty, and it should not contain the '=' character, as with other environment-modifying interfaces.

In shell environments such as Bash, the built-in command unset VAR removes VAR from the environment for the current session; the effect is that this variable will not be inherited by subsequently started processes. Different shells may have variations in syntax and behavior, but the underlying concept remains the same: the variable is no longer visible to new programs launched from that shell.

Implementation details and portability: The process environment is typically represented as an array of strings of the form NAME=value; removing a variable requires locating its entry, removing it from the array, and freeing any allocated memory. Portability differs across platforms; Windows uses different APIs (such as SetEnvironmentVariable), and environment handling varies between processes and threads.

Security and usage notes: Removing sensitive variables like PATH or LD_LIBRARY_PATH can affect program behavior and system security. Unset variables only when their removal is understood and safe for the running application and its child processes.

See also: unsetenv, setenv, getenv, environ, putenv.