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About Break

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

SHORT DESCRIPTION

Describes a statement you can use to immediately exit Foreach, For, While, Do, or Switch statements.

LONG DESCRIPTION

When a Break statement appears in a loop, such as a Foreach, For, Switch, or While loop, the Break statement causes Windows PowerShell to immediately exit the loop. In a Switch construct that does not loop, Break causes Windows PowerShell to exit the Switch code block.

A Break statement can include a label that lets you exit embedded loops. A label can specify any loop keyword, such as Foreach, For, or While, in a script. When you use a label, Break exits the specified loop. Break exits the specified loop, regardless of which loop the Break statement is in.

The following example shows how to use a Break statement to exit a For statement:

for($i=1; $i -le 10; $i++)
{
   Write-Host $i
   break
}

In this example, the Break statement exits the For loop when the $i variable equals 1. Even though the For statement evaluates to True until $i is greater than 10, Windows PowerShell reaches the break statement the first time the For loop is run.

It is more common to use the Break statement in a loop where an inner condition must be met. Consider the following Foreach statement example:

$i=0
$varB = 10,20,30,40
foreach ($val in $varB)
{
   $i++
   if ($val -eq 30)
   {
     break
    }
   }
Write-Host "30 was found in array position $i"

In this example, the Foreach statement iterates the $varB array. Each time the code block is run, the $i variable is incremented by 1. The If statement evaluates to False the first two times the loop is run. The third time the loop is run, $i equals 3, and the $val variable equals 30. At this point, the Break statement runs, and the Foreach loop exits.

You break out of the other looping statements in the same way you break out of the Foreach loop. In the following example, the Break statement exits a While statement when a DivideByZeroException exception is trapped using the Trap statement.

$i = 3
while ($true)
{
   trap [DivideByZeroException]
   {
      Write-Host "divide by zero trapped"
      break
   }
   1 / $i--
}

A Break statement can include a label. If you use the Break keyword with a label, Windows PowerShell exits the labeled loop instead of exiting the current loop. The syntax for a label is as follows (this example shows a label in a While loop):

:myLabel while (<condition>) { <statement list>}

The label is a colon followed by a name that you assign. The label must be the first token in a statement, and it must be followed by the looping keyword, such as While.

In Windows PowerShell, only loop keywords, such as Foreach, For, and While can have a label.

Break moves execution out of the labeled loop. In embedded loops, this has a different result than the Break keyword has when it is used by itself. This schematic example has a While statement with a For statement:

:myLabel while (<condition 1>)
{
   for ($item in $items)
   {
      if (<condition 2>) { break myLabel }
      $item = $x   # A statement inside the For-loop
   }
}
$a = $c  # A statement after the labeled While-loop

If condition 2 evaluates to True, the execution of the script skips down to the statement after the labeled loop. In the example, execution starts again with the statement "$a = $c".

You can nest many labeled loops, as shown in the following schematic example.

:red while (<condition1>)
{
   :yellow while (<condition2>)
   {
      while (<condition3>)
      {
         if ($a) {break}
         if ($b) {break red}
         if ($c) {break yellow}
      }
      After innermost loop
    }
    After "yellow" loop
}
After "red" loop

If the $b variable evaluates to True, execution of the script resumes after the loop that is labeled "red". If the $c variable evaluates to True, execution of the script control resumes after the loop that is labeled "yellow".

If the $a variable evaluates to True, execution resumes after the innermost loop. No label is needed.

Windows PowerShell does not limit how far labels can resume execution. The label can even pass control across script and function call boundaries.

The Break keyword is used to leave the Switch construct. For example, the following Switch statement uses Break statements to test for the most specific condition:

$var = "word2"
switch -regex ($var)
{
   "word2"
  {
     Write-Host "Exact" $_
     break
   }

   "word.*"
   {
      Write-Host "Match on the prefix" $_
      break
  }

  "w.*"
  {
    Write-Host "Match on at least the first letter" $_
    break
  }

  default
  {
     Write-Host "No match" $_
    break
  }
}

In this example, the $var variable is created and initialized to a string value of "word2". The Switch statement uses the Regex class to match the variable value first with the term "word2". (The Regex class is a regular expression Microsoft .NET Framework class.) Because the variable value and the first test in the Switch statement match, the first code block in the Switch statement runs.

When Windows PowerShell reaches the first Break statement, the Switch statement exits. If the four Break statements are removed from the example, all four conditions are met. This example uses the break statement to display results when the most specific condition is met.

SEE ALSO

about_Comparison_Operators about_Continue about_For about_Foreach about_Switch about_Throw about_Trap about_Try_Catch_Finally about_While

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