unalias man page


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.

unalias — remove alias definitions


unalias alias-name...

unalias -a


The unalias utility shall remove the definition for each alias name specified. See Section 2.3.1, Alias Substitution. The aliases shall be removed from the current shell execution environment; see Section 2.12, Shell Execution Environment.


The unalias utility shall conform to the Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.

The following option shall be supported:


Remove all alias definitions from the current shell execution environment.


The following operand shall be supported:


The name of an alias to be removed.


Not used.

Input Files


Environment Variables

The following environment variables shall affect the execution of unalias:


Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1‐2008, Section 8.2, Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)


If set to a non-empty string value, override the values of all the other internationalization variables.


Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multi-byte characters in arguments).


Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.


Determine the location of message catalogs for the processing of LC_MESSAGES.

Asynchronous Events



Not used.


The standard error shall be used only for diagnostic messages.

Output Files


Extended Description


Exit Status

The following exit values shall be returned:


Successful completion.


One of the alias-name operands specified did not represent a valid alias definition, or an error occurred.

Consequences of Errors


The following sections are informative.

Application Usage

Since unalias affects the current shell execution environment, it is generally provided as a shell regular built-in.




The unalias description is based on that from historical KornShell implementations. Known differences exist between that and the C shell. The KornShell version was adopted to be consistent with all the other KornShell features in this volume of POSIX.1‐2008, such as command line editing.

The -a option is the equivalent of the unalias * form of the C shell and is provided to address security concerns about unknown aliases entering the environment of a user (or application) through the allowable implementation-defined predefined alias route or as a result of an ENV file. (Although unalias could be used to simplify the “secure” shell script shown in the command rationale, it does not obviate the need to quote all command names. An initial call to unalias -a would have to be quoted in case there was an alias for unalias.)

Future Directions


See Also

Chapter 2, Shell Command Language, alias

The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines


2013 IEEE/The Open Group POSIX Programmer's Manual