# unset

## PROLOG



           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.
    


## NAME



           unset — unset values and attributes of variables and functions
    


## SYNOPSIS



           unset **[** -fv**]**_name_...
    


## DESCRIPTION



           Each variable or function specified by _name_ shall be unset.
    
           If **-v** is specified, _name_ refers to a variable name and the shell
           shall unset it and remove it from the environment. Read-only
           variables cannot be unset.
    
           If **-f** is specified, _name_ refers to a function and the shell shall
           unset the function definition.
    
           If neither **-f** nor **-v** is specified, _name_ refers to a variable; if a
           variable by that name does not exist, it is unspecified whether a
           function by that name, if any, shall be unset.
    
           Unsetting a variable or function that was not previously set shall
           not be considered an error and does not cause the shell to abort.
    
           The _unset_ special built-in shall support the Base Definitions
           volume of POSIX.1‐2017, _Section 12.2_ , _Utility Syntax Guidelines_.
    
           Note that:
    
               VARIABLE=
    
           is not equivalent to an _unset_ of **VARIABLE** ; in the example,
           **VARIABLE** is set to **""**.  Also, the variables that can be _unset_
           should not be misinterpreted to include the special parameters
           (see _Section 2.5.2_ , _Special Parameters_).
    


## OPTIONS



           See the DESCRIPTION.
    


## OPERANDS



           See the DESCRIPTION.
    


## STDIN



           Not used.
    


## INPUT FILES



           None.
    


## ENVIRONMENT VARIABLES



           None.
    


## ASYNCHRONOUS EVENTS



           Default.
    


## STDOUT



           Not used.
    


## STDERR



           The standard error shall be used only for diagnostic messages.
    


## OUTPUT FILES



           None.
    


## EXTENDED DESCRIPTION



           None.
    


## EXIT STATUS



            0    All _name_ operands were successfully unset.
    
           >0    At least one _name_ could not be unset.
    


## CONSEQUENCES OF ERRORS



           Default.
    
           _The following sections are informative._
    


## APPLICATION USAGE



           None.
    


## EXAMPLES



           Unset _VISUAL_ variable:
    
               unset -v VISUAL
    
           Unset the functions **foo** and **bar** :
    
               unset -f foo bar
    


## RATIONALE



           Consideration was given to omitting the **-f** option in favor of an
           _unfunction_ utility, but the standard developers decided to retain
           historical practice.
    
           The **-v** option was introduced because System V historically used
           one name space for both variables and functions. When _unset_ is
           used without options, System V historically unset either a
           function or a variable, and there was no confusion about which one
           was intended.  A portable POSIX application can use _unset_ without
           an option to unset a variable, but not a function; the **-f** option
           must be used.
    


## FUTURE DIRECTIONS



           None.
    


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