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about_Do

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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 statement 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. For more information about how booleans are evaluated, see about_Booleans.

Example

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

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

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