unset(1) [linux man page]
UNSET(P) POSIX Programmer's Manual UNSET(P) 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 func- tion 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 IEEE Std 1003.1-2001, 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 mis- interpreted to include the special parameters (see 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 histori- cal 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. SEE ALSO
Special Built-In Utilities COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 . IEEE
/The Open Group 2003 UNSET(P)
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EXPORT(P) POSIX Programmer's Manual EXPORT(P) NAME
export - set the export attribute for variables SYNOPSIS
export name[=word]... export -p DESCRIPTION
The shell shall give the export attribute to the variables corresponding to the specified names, which shall cause them to be in the envi- ronment of subsequently executed commands. If the name of a variable is followed by = word, then the value of that variable shall be set to word. The export special built-in shall support the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines. When -p is specified, export shall write to the standard output the names and values of all exported variables, in the following format: "export %s=%s ", <name>, <value> if name is set, and: "export %s ", <name> if name is unset. The shell shall format the output, including the proper use of quoting, so that it is suitable for reinput to the shell as commands that achieve the same exporting results, except: 1. Read-only variables with values cannot be reset. 2. Variables that were unset at the time they were output need not be reset to the unset state if a value is assigned to the variable between the time the state was saved and the time at which the saved output is reinput to the shell. When no arguments are given, the results are unspecified. OPTIONS
See the DESCRIPTION. OPERANDS
See the DESCRIPTION. STDIN
Not used. INPUT FILES
None. ENVIRONMENT VARIABLES
None. ASYNCHRONOUS EVENTS
Default. STDOUT
See the DESCRIPTION. STDERR
The standard error shall be used only for diagnostic messages. OUTPUT FILES
None. EXTENDED DESCRIPTION
None. EXIT STATUS
Zero. CONSEQUENCES OF ERRORS
Default. The following sections are informative. APPLICATION USAGE
None. EXAMPLES
Export PWD and HOME variables: export PWD HOME Set and export the PATH variable: export PATH=/local/bin:$PATH Save and restore all exported variables: export -p > temp-fileunset a lot of variables... processing. temp-file RATIONALE
Some historical shells use the no-argument case as the functional equivalent of what is required here with -p. This feature was left unspecified because it is not historical practice in all shells, and some scripts may rely on the now-unspecified results on their imple- mentations. Attempts to specify the -p output as the default case were unsuccessful in achieving consensus. The -p option was added to allow portable access to the values that can be saved and then later restored using; for example, a dot script. FUTURE DIRECTIONS
None. SEE ALSO
Special Built-In Utilities COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 . IEEE
/The Open Group 2003 EXPORT(P)