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About Switch

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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 statement 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.

The Switch statement also uses the $switch automatic variable. For more information, see about_Automatic_Variables.

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.

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.

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.

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.

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.

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

or

switch [-regex|-wildcard|-exact][-casesensitive] -file filename
{
    "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:

Parameter Description
Wildcard Indicates that the condition is a wildcard string.
If the match clause is not a string, the parameter is
ignored.
Exact Indicates that the match clause, if it is a string, must
match exactly. If the match clause is not a string, this parameter
is ignored.
CaseSensitive Performs 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.
Regex Performs regular expression matching of the value to the
condition. If the
match clause is not a string, this parameter is ignored.

Note

When specifying conflicting values, like Regex and Wildcard, the last parameter specified takes precedence, and all conflicting parameters are ignored. Multiple instances of parameters are also permitted. However, only the last parameter used is effective.

In this example, there is no matching case so there is no output.

switch ("fourteen")
{
    1 {"It is one."; Break}
    2 {"It is two."; Break}
    3 {"It is three."; Break}
    4 {"It is four."; Break}
    "fo*" {"That's too many."}
}

By adding the Default clause, you can perform an action when no other conditions succeed.

switch ("fourteen")
{
    1 {"It is one."; Break}
    2 {"It is two."; Break}
    3 {"It is three."; Break}
    4 {"It is four."; Break}
    "fo*" {"That's too many."}
    Default {
        "No matches"
    }
}

No matches

For the word "fourteen" to match a case you must use the -Wildcard or -Regex parameter.

   PS> switch -Wildcard ("fourteen")
       {
           1 {"It is one."; Break}
           2 {"It is two."; Break}
           3 {"It is three."; Break}
           4 {"It is four."; Break}
           "fo*" {"That's too many."}
       }

That's too many.

The following example uses the -Regex parameter.

$target = 'user@contoso.com'
switch -Regex ($target)
{
    'ftp\://.*' { "$_ is an ftp address"; Break }
    '\w+@\w+\.com|edu|org' { "$_ is an email address"; Break }
    'http[s]?\://.*' { "$_ is a web address"; Break }
}

user@contoso.com is an email address

A Switch statement condition may be either:

  • An expression whose value is compared to the input value
  • A script block which should return $true if a condition is met. The script block receives the current object to compare in the $_ automatic variable and is evaluated in its own scope.

The action for each condition is independent of the actions in other conditions.

The following example demonstrates the use of script blocks as Switch statement conditions.

switch ("Test")
{
    {$_ -is [String]} {
        "Found a string"
    }
    "Test" {
        "This executes as well"
    }
}

Found a string
This executes as well

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 stops processing the current value, but continues processing any subsequent values.

The following example processes an array of numbers and displays if they are odd or even. Negative numbers are skipped with the Continue keyword. If a non-number is encountered, execution is terminated with the Break keyword.

switch (1,4,-1,3,"Hello",2,1)
{
    {$_ -lt 0} { Continue }
    {$_ -isnot [Int32]} { Break }
    {$_ % 2} {
        "$_ is Odd"
    }
    {-not ($_ % 2)} {
        "$_ is Even"
    }
}

1 is Odd
4 is Even
3 is Odd

SEE ALSO

about_Break

about_Continue

about_If

about_Script_Blocks