Explains how to use a switch to handle multiple If statements. (about_Switch)
TOPICabout_SwitchSHORT DESCRIPTIONExplains how to use a switch to handle multiple If statements.LONG DESCRIPTIONYou 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 C:\Windows>powershell get-help about_Throw -full
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