about_Switch

TOPIC
	about_Switch

SHORT DESCRIPTION
	Explains how to use a switch to handle multiple If statements.

LONG DESCRIPTION
	You use an If statement to make a decision in a script or program. 
	Essentially, it says; “If this condition exists, perform this action. 
	Otherwise do that action.” You can perform that operation as many 
	times as you want, but if you have a long list of conditions, an If 
	statement becomes unwieldy. You can combine a long list of conditions
	in a switch statement. As in all branching statements, braces ({}) 
	must enclose script blocks.

	A Switch statement is, in effect, a series of If statements. It matches 
	the expression with each of the conditions case by case. If a match 
	is found, the action associated with that condition is performed. A 
	basic switch statement takes the following form:

		PS> $a = 3
		PS> switch ($a) {
			1 {"It is one."}
			2 {"It is two."}
			3 {"It is three."}
			4 {"It is four."}
		}
	
		It is three.


	This simple example takes a value and compares it with each condition 
	in the list. The action echoes a string from the match. But, you 
	could have a problem if you check all of the conditions. 
	For example:

		PS> $day = "day5"
		PS> switch ($day){
			day1 {"Monday"; break}
			day2 {"Tuesday"; break}
			day3 {"Wednesday"; break}
			day4 {"Thursday"; break}
			day5 {"Friday"; break}
			day6 {"Saturday"; break}
			day7 {"Sunday"; break}
			day5 {"Too many days"; break}
		}
	
		Friday


	There are two day5 conditions in the list. But, the break at the end of 
	each condition tells the switch to stop looking further and to perform 
	the action it finds. If the break statements were not there, both 
	day5 actions would be performed. 

	If the value to switch against is an array, then each element in the 
	array will be evaluated in order, starting at element 0 (zero). At least 
	one element must be present that meets at least one condition; otherwise, 
	an error will result. If there is more than one default clause, an 
	error will result.

	The complete switch syntax is as follows:

		switch [-regex|-wildcard|-exact][-casesensitive] ( pipeline )

	or

		switch [-regex|-wildcard|-exact][-casesensitive] -file filename

	followed by

		{ 
			"string"|number|variable|{ expression } { statementlist }
			default { statementlist } 
	}


	By default, if no parameters are used, Switch behaves as if a case- 
	insensitive exact match is in effect. If "pipeline" results in an 
	array, each element of the array will be evaluated in ascending offset 
	order (starting at 0 [zero]).   

	At least one conditional element must be present in the Switch 
	codeblock, and only one default clause can be present. If more than 
	one default clause is present, a ParseException will be thrown.

	Switch has the following parameters:

		Regex		 Indicates that the match clause, if it is a string, is 
						treated as a regex string. Use of this parameter 
						disables Wildcard and Exact. If the match clause is not
						a string, this parameter is ignored.

		Wildcard		Indicates that the match clause, if it is a string, is 
						treated as a wildcard string. Use of this 
						parameter disables Regex and Exact. If the match clause
						is not a string, this parameter is ignored.

		Exact		 Indicates that the match clause, if it is a string, must 
						match exactly. Use of this parameter disables 
						Wildcard and Regex. If the match clause is not a 
						string, this parameter is ignored.

		CaseSensitive   Modifies the match clause, if it is a string, to be
						case-sensitive. If the match clause is not a string,
						this parameter is ignored.

		File			Takes input from a file (or representative) rather 
						than a statement. If multiple File parameters are 
						used, the last one is used. Each line of the 
						file is read and passed through the switch block.

	Multiple uses of Regex, Wildcard, or Exact are allowed. However, only 
	the last parameter used governs the behavior.

	The Break keyword indicates that no more processing will occur and 
	that the Switch statement will exit.  

	The Continue keyword indicates that no processing will continue 
	against the current token and that the next token in the conditional will 
	be evaluated. If no tokens are available, the Switch statement will 
	exit.

	The "{ expression }" block may be a code block that will be evaluated 
	at the time of the comparison. The current object is bound to 
	the $_ automatic variable and is available during the evaluation of 
	the expression. A comparison is considered a match if the expression 
	evaluates to "True".  This expression is evaluated in a new scope.

	The "Default" keyword within the switch statement indicates that if 
	no matches are found, the code block that follows the keyword will 
	be evaluated. Program flow will not be allowed from block to 
	block because the closing brace ( } ) in the compound list is an explicit 
	break. 

	If multiple matches are found, each match results in the 
	expression being executed. To avoid this, the Break or Continue 
	keywords can be used to halt further comparisons.


SEE ALSO
	about_Break
	about_Continue
	about_If
	about_Script_Blocks