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Full Discussion: return ${1-0}
Top Forums UNIX for Dummies Questions & Answers return ${1-0} Post 302186616 by era on Thursday 17th of April 2008 02:51:20 PM
Old 04-17-2008
If $1 is unset, return 0, otherwise return $1

The general form is ${var-value}; see also ${var+value} and ${var?value} in the documentation for your shell.
 

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ISSET(3)								 1								  ISSET(3)

isset - Determine if a variable is set and is not NULL

SYNOPSIS
bool isset (mixed $var, [mixed $...]) DESCRIPTION
Determine if a variable is set and is not NULL. If a variable has been unset with unset(3), it will no longer be set. isset(3) will return FALSE if testing a variable that has been set to NULL. Also note that a null character ( "") is not equivalent to the PHP NULL constant. If multiple parameters are supplied then isset(3) will return TRUE only if all of the parameters are set. Evaluation goes from left to right and stops as soon as an unset variable is encountered. PARAMETERS
o $var - The variable to be checked. o $... - Another variable ... RETURN VALUES
Returns TRUE if $var exists and has value other than NULL, FALSE otherwise. CHANGELOG
+--------+---------------------------------------------------+ |Version | | | | | | | Description | | | | +--------+---------------------------------------------------+ | 5.4.0 | | | | | | | Checking non-numeric offsets of strings now | | | returns FALSE. | | | | +--------+---------------------------------------------------+ EXAMPLES
Example #1 isset(3) Examples <?php $var = ''; // This will evaluate to TRUE so the text will be printed. if (isset($var)) { echo "This var is set so I will print."; } // In the next examples we'll use var_dump to output // the return value of isset(). $a = "test"; $b = "anothertest"; var_dump(isset($a)); // TRUE var_dump(isset($a, $b)); // TRUE unset ($a); var_dump(isset($a)); // FALSE var_dump(isset($a, $b)); // FALSE $foo = NULL; var_dump(isset($foo)); // FALSE ?> This also work for elements in arrays: <?php $a = array ('test' => 1, 'hello' => NULL, 'pie' => array('a' => 'apple')); var_dump(isset($a['test'])); // TRUE var_dump(isset($a['foo'])); // FALSE var_dump(isset($a['hello'])); // FALSE // The key 'hello' equals NULL so is considered unset // If you want to check for NULL key values then try: var_dump(array_key_exists('hello', $a)); // TRUE // Checking deeper array values var_dump(isset($a['pie']['a'])); // TRUE var_dump(isset($a['pie']['b'])); // FALSE var_dump(isset($a['cake']['a']['b'])); // FALSE ?> Example #2 isset(3) on String Offsets PHP 5.4 changes how isset(3) behaves when passed string offsets. <?php $expected_array_got_string = 'somestring'; var_dump(isset($expected_array_got_string['some_key'])); var_dump(isset($expected_array_got_string[0])); var_dump(isset($expected_array_got_string['0'])); var_dump(isset($expected_array_got_string[0.5])); var_dump(isset($expected_array_got_string['0.5'])); var_dump(isset($expected_array_got_string['0 Mostel'])); ?> Output of the above example in PHP 5.3: bool(true) bool(true) bool(true) bool(true) bool(true) bool(true) Output of the above example in PHP 5.4: bool(false) bool(true) bool(true) bool(true) bool(false) bool(false) NOTES
Warning isset(3) only works with variables as passing anything else will result in a parse error. For checking if constants are set use the defined(3) function. Note Because this is a language construct and not a function, it cannot be called using variable functions. Note When using isset(3) on inaccessible object properties, the __isset() overloading method will be called, if declared. SEE ALSO
empty(3), __isset(), unset(3), defined(3), the type comparison tables, array_key_exists(3), is_null(3), the error control @ operator. PHP Documentation Group ISSET(3)
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