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about_Do

Updated: May 8, 2014

Applies To: Windows PowerShell 2.0, Windows PowerShell 3.0, Windows PowerShell 4.0

TOPIC
    about_Do

SHORT DESCRIPTION
    Runs a statement list one or more times, subject to a While or Until 
    condition.


LONG DESCRIPTION
    The Do keyword works with the While keyword or the Until keyword to run 
    the statements in a script block, subject to a condition. Unlike the 
    related While loop, the script block in a Do loop always runs at least 
    once.


    A Do-While loop is a variety of the While loop. In a Do-While loop, the 
    condition is evaluated after the script block has run. As in a While loop,
    the script block is repeated as long as the condition evaluates to true. 


    Like a Do-While loop, a Do-Until loop always runs at least once before 
    the condition is evaluated. However, the script block runs only while
    the condition is false. 


    The Continue and Break flow control keywords can be used in a Do-While 
    loop or in a Do-Until loop.  


  Syntax
      The following shows the syntax of the Do-While statement:


          do {<statement list>} while (<condition>)


      The following shows the syntax of the Do-Until statement:


          do {<statement list>} until (<condition>)


      The statment list contains one or more statements that run each time
      the loop is entered or repeated.


      The condition portion of the statement resolves to true or false. 


  Example
      The following example of a Do statement counts the items in an 
      array until it reaches an item with a value of 0.


          C:\PS> $x = 1,2,78,0
          C:\PS> do { $count++; $a++; } while ($x[$a] -ne 0) 
          C:\PS> $count
          3


      The following example uses the Until keyword. Notice that
      the not equal to operator (-ne) is replaced by the 
      equal to operator (-eq).


          C:\PS> $x = 1,2,78,0
          C:\PS> do { $count++; $a++; } until ($x[$a] -eq 0) 
          C:\PS> $count
          3


      The following example writes all the values of an array, skipping any
      value that is less than zero.


          do
          {
              if ($x[$a] -lt 0) { continue }
              Write-Host $x[$a]
          } 
          while (++$a -lt 10)


SEE ALSO
    about_While
    about_Operators
    about_Assignment_Operators
    about_Comparison_Operators
    about_Break
    about_Continue



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