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About Switch

JuanPablo Jofre|Last Updated: 11/17/2016
|
2 Contributors

about_Switch

SHORT DESCRIPTION

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

LONG DESCRIPTION

To check a condition in a script or function, use an If statement. The If can check many types of conditions, including the value of variables and the properties of objects.

To check multiple conditions, use a Switch statement. The Switch statement is equivalent to a series of If statements, but it is simpler. The Switch statement lists each condition and an optional action. If a condition obtains, the action is performed.

A basic Switch statement has the following format:

Switch (<test-value>)  
 {  
     <condition> {<action>}  
     <condition> {<action>}  
}

For example, the following Switch statement compares the test value, 3, to each of the conditions. When the test value matches the condition, the action is performed.

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

In this simple example, the value is compared to each condition in the list, even though there is a match for the value 3. The following Switch statement has two conditions for a value of 3. It demonstrates that, by default, all conditions are tested.

PS> switch (3)   
 {  
    1 {"It is one."}  
    2 {"It is two."}  
    3 {"It is three."}  
    4 {"It is four."}  
    3 {"Three again."}  
 }   
It is three.  
Three again.

To direct the Switch to stop comparing after a match, use the Break statement. The Break statement terminates the Switch statement.

PS> switch (3)   
 {  
    1 {"It is one."}  
    2 {"It is two."}  
    3 {"It is three."; Break}  
    4 {"It is four."}  
    3 {"Three again."}  
 }   
It is three.

If the test value is a collection, such as an array, each item in the collection is evaluated in the order in which it appears. The following examples evaluates 4 and then 2.

PS> switch (4, 2)   
 {  
    1 {"It is one." }  
    2 {"It is two." }  
    3 {"It is three." }  
    4 {"It is four." }  
    3 {"Three again."}  
 }   
It is four.  
It is two.

Any Break statements apply to the collection, not to each value, as shown in the following example. The Switch statement is terminated by the Break statement in the condition of value 4.

PS> switch (4, 2)   
 {  
    1 {"It is one."; Break}  
    2 {"It is two." ; Break }  
    3 {"It is three." ; Break }  
    4 {"It is four." ; Break }  
    3 {"Three again."}  
 }   
It is four.

SYNTAX

The complete Switch statement syntax is as follows:

switch [-regex|-wildcard|-exact][-casesensitive] (<value>)

or

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

followed by

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

If no parameters are used, Switch performs a case-insensitive exact match for the value. If the value is a collection, each element is evaluated in the order in which it appears.

The Switch statement must include at least one condition statement.

The Default clause is triggered when the value does not match any of the conditions. It is equivalent to an Else clause in an If statement. Only one Default clause is permitted in each Switch statement.

Switch has the following parameters:

Regex      Performs regular expression matching of the   
                value to the condition. If you use Regex,  
                Wildcard and Exact are ignored. Also, if the   
                match clause is not a string, this parameter   
                is ignored.
Example:  
   PS> switch ("fourteen")   
       {  
           1 {"It is one."; Break}  
           2 {"It is two."; Break}  
           3 {"It is three."; Break}  
           4 {"It is four."; Break}  
           3 {"Three again."; Break}  
           "fo*" {"That's too many."}  
       }   

   PS> switch -Regex ("fourteen")   
       {  
           1 {"It is one."; Break}  
           2 {"It is two."; Break}  
           3 {"It is three."; Break}  
           4 {"It is four."; Break}  
           3 {"Three again."; Break}  
           "fo*" {"That's too many."}  
       }  
That's too many.
Wildcard      Indicates that the condition is a wildcard string.   
                If you use Wildcard, Regex and Exact are ignored.   
                Also, 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. If you use Exact, Regex and   
                Wildcard and Exact are ignored. Also, if the match   
                clause is not a string, this parameter is ignored.  

CaseSensitivePerforms a case-sensitive match. If the match   
                clause is not a string, this parameter is ignored.  

File      Takes input from a file rather than a value   
                statement. If multiple File parameters are   
                included, only the last one is used. Each line of the   
                file is read and evaluated by the Switch statement.

Multiple instances of Regex, Wildcard, or Exact are permitted. However, only the last parameter used is effective.

If the value matches multiple conditions, the action for each condition is executed. To change this behavior, use the Break or Continue keywords.

The Break keyword stops processing and exits the Switch statement.

The Continue keyword continues processing the current value and any subsequent values.

If the condition is an expression or a script block, it is evaluated just before it is compared to the value. The value is assigned to the $_ automatic variable and is available in the expression. The match succeeds if the expression is true or matches the value. The expression is evaluated in its own scope.

The "Default" keyword specifies a condition that is evaluated only when no other conditions match the value.

The action for each condition is independent of the actions in other conditions. The closing brace ( } ) in the action is an explicit break.

SEE ALSO

about_Break

about_Continue

about_If

about_Script_Blocks

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