8. Switch statement¶

Note

The below information is extensively based in information taken from the PowerShell® Notes for Professionals book. I plan to extend this information based on my day to day usage of the language.

A switch statement allows a variable to be tested for equality against a list of values. Each value is called a case , and the variable being switched on is checked for each switch case. It enables you to write a script that can choose from a series of options, but without requiring you to write a long series of if statements.

8.1: Simple Switch¶

Switch statements compare a single test value to multiple conditions, and performs any associated actions for successful comparisons. It can result in multiple matches/actions.

Given the following switch...

switch($myValue)
{
  'First Condition' { 'First Action' }
  'Second Condition' { 'Second Action' }
}

'First Action' will be output if $myValue is set as 'First Condition'.

'Action' will be output if $myValue is set as 'Second Condition'.

Nothing will be output if $myValue does not match either conditions.

8.2: Switch Statement with CaseSensitive Parameter¶

The -CaseSensitive parameter enforces switch statements to perform exact, case-sensitive matching against conditions.

Example:

switch -CaseSensitive ('Condition')
{
  'condition' {'First Action'}
  'Condition' {'Second Action'}
  'condition' {'Third Action'}
}

Output:

1	Second Action

The second action is the only action executed because it is the only condition that exactly matches the string 'Condition' when accounting for case-sensitivity.

8.3: Switch Statement with Wildcard Parameter¶

The -Wildcard parameter allows switch statements to perform wildcard matching against conditions.

Example:

switch -Wildcard ('Condition')
{
  'Condition' {'Normal match'}
  'Condit*' {'Zero or more wildcard chars.'}
  'C[aoc]ndit[f-l]on' {'Range and set of chars.'}
  'C?ndition' {'Single char. wildcard'}
  'Test*' {'No match'}
}

Output:

Normal match
Zero or more wildcard chars.
Range and set of chars.
Single char. wildcard

8.4: Switch Statement with File Parameter¶

The -file parameter allows the switch statement to receive input from a file. Each line of the file is evaluated by the switch statement.

Example file input.txt:

1 2	condition test

Example switch statement:

switch -file input.txt
{
  'condition' {'First Action'}
  'test' {'Second Action'}
  'fail' {'Third Action'}
}

Output:

1 2	First Action Second Action

8.5: Simple Switch with Default Condition¶

The Default keyword is used to execute an action when no other conditions match the input value.

Example:

switch('Condition')
{
  'Skip Condition'
  {
    'First Action'
  }
  'Skip This Condition Too'
  {
    'Second Action'
  }
  Default
  {
    'Default Action'
  }
}

Output:

1	Default Action

8.6: Switch Statement with Regex Parameter¶

The -Regex parameter allows switch statements to perform regular expression matching against conditions.

Example:

switch -Regex ('Condition')
{
  'Con\D+ion' {'One or more non-digits'}
  'Conditio*$' {'Zero or more "o"'}
  'C.ndition' {'Any single char.'}
  '^C\w+ition$' {'Anchors and one or more word chars.'}
  'Test' {'No match'}
}

Output:

1
2
3

One or more non-digits
Any single char.
Anchors and one or more word chars.

8.7: Simple Switch With Break¶

The break keyword can be used in switch statements to exit the statement before evaluating all conditions.

Example:

switch('Condition')
{
  'Condition'
  {
    'First Action'
  }
  'Condition'
  {
    'Second Action'
    break
  }
  'Condition'
  {
    'Third Action'
  }
}

Output:

1 2	First Action Second Action

Because of the break keyword in the second action, the third condition is not evaluated.

8.8: Switch Statement with Exact Parameter¶

The -Exact parameter enforces switch statements to perform exact, case-insensitive matching against string conditions.

Example:

switch -Exact ('Condition')
{
  'condition' {'First Action'}
  'Condition' {'Second Action'}
  'conditioN' {'Third Action'}
  '^*ondition$' {'Fourth Action'}
  'Conditio*' {'Fifth Action'}
}

Output:

1
2
3

First Action
Second Action
Third Action

The first through third actions are executed because their associated conditions matched the input. The regex and wildcard strings in the fourth and fifth conditions fail matching.

Note that the fourth condition would also match the input string if regular expression matching was being performed, but was ignored in this case because it is not.

8.9: Switch Statement with Expressions¶

Conditions can also be expressions:

1	$myInput = 0

switch($myInput) {
  # because the result of the expression, 4,
  # does not equal our input this block should not be run.
  ( 2 + 2 ) { 'True. 2 +2 = 4' }

  # because the result of the expression, 0,
  # does equal our input this block should be run.
  ( 2 - 2 ) { 'True. 2-2 = 0' }

  # because our input is greater than -1 and is less than 1
  # the expression evaluates to true and the block should be run.
  { $_ -gt - 1 -and $_ -lt 1 } { 'True. Value is 0' }
}

1
2
3

#Output
True. 2 - 2 = 0
True. Value is 0