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This article is about Unix command. For the town in Hedmark, see Unset, Norway. For the novelist, see Sigrid Undset.

unset is a builtin command implemented by both the Bourne shell family (sh, ksh, bash, etc.) and the C shell family (csh, tcsh, etc.) of Unix command line shells. It unsets a shell variable, removing it from memory and the shell's exported environment. It is implemented as a shell builtin, because it directly manipulates the internals of the shell.

Read-only shell variables cannot be unset. If one tries to unset a read-only variable, the unset command will print an error message and return a non-zero exit code.

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