unset(3) [php man page]
UNSET(3) 1 UNSET(3) unset - Unset a given variable SYNOPSIS
void unset (mixed $var, [mixed $...]) DESCRIPTION
unset(3) destroys the specified variables. The behavior of unset(3) inside of a function can vary depending on what type of variable you are attempting to destroy. If a globalized variable is unset(3) inside of a function, only the local variable is destroyed. The variable in the calling environment will retain the same value as before unset(3) was called. <?php function destroy_foo() { global $foo; unset($foo); } $foo = 'bar'; destroy_foo(); echo $foo; ?> The above example will output: bar To unset(3) a global variable inside of a function, then use the $GLOBALS array to do so: <?php function foo() { unset($GLOBALS['bar']); } $bar = "something"; foo(); ?> If a variable that is PASSED BY REFERENCE is unset(3) inside of a function, only the local variable is destroyed. The variable in the calling environment will retain the same value as before unset(3) was called. <?php function foo(&$bar) { unset($bar); $bar = "blah"; } $bar = 'something'; echo "$bar "; foo($bar); echo "$bar "; ?> The above example will output: something something If a static variable is unset(3) inside of a function, unset(3) destroys the variable only in the context of the rest of a function. Fol- lowing calls will restore the previous value of a variable. <?php function foo() { static $bar; $bar++; echo "Before unset: $bar, "; unset($bar); $bar = 23; echo "after unset: $bar "; } foo(); foo(); foo(); ?> The above example will output: Before unset: 1, after unset: 23 Before unset: 2, after unset: 23 Before unset: 3, after unset: 23 PARAMETERS
o $var - The variable to be unset. o $... - Another variable ... RETURN VALUES
No value is returned. EXAMPLES
Example #1 unset(3) example <?php // destroy a single variable unset($foo); // destroy a single element of an array unset($bar['quux']); // destroy more than one variable unset($foo1, $foo2, $foo3); ?> Example #2 Using (unset) casting (unset) casting is often confused with the unset(3) function. (unset) casting serves only as a NULL-type cast, for completeness. It does not alter the variable it's casting. <?php $name = 'Felipe'; var_dump((unset) $name); var_dump($name); ?> The above example will output: NULL string(6) "Felipe" NOTES
Note Because this is a language construct and not a function, it cannot be called using variable functions. Note It is possible to unset even object properties visible in current context. Note It is not possible to unset $this inside an object method since PHP 5. Note When using unset(3) on inaccessible object properties, the __unset() overloading method will be called, if declared. SEE ALSO
isset(3), empty(3), __unset(), array_splice(3). PHP Documentation Group UNSET(3)
Check Out this Related 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)