about_Continue

Artikkeli
09/19/2022

Short description

Describes how the continue statement immediately returns the program flow to the top of a program loop, a switch statement, or a trap statement.

Long description

The continue statement provides a way to exit the current control block but continue execution, rather than exit completely. The statement supports labels. A label is a name you assign to a statement in a script.

Using continue in loops

An unlabeled continue statement immediately returns the program flow to the top of the innermost loop that is controlled by a for, foreach, do, or while statement. The current iteration of the loop is terminated and the loop continues with the next iteration.

In the following example, program flow returns to the top of the while loop if the $ctr variable is equal to 5. As a result, all the numbers between 1 and 10 are displayed except for 5:

while ($ctr -lt 10)
{
    $ctr += 1
    if ($ctr -eq 5)
    {
        continue
    }

    Write-Host -Object $ctr
}

When using a for loop, execution continues at the <Repeat> statement, followed by the <Condition> test. In the example below, an infinite loop will not occur because the decrement of $i occurs after the continue keyword.

#   <Init>  <Condition> <Repeat>
for ($i = 0; $i -lt 10; $i++)
{
    Write-Host -Object $i
    if ($i -eq 5)
    {
        continue
        # Will not result in an infinite loop.
        $i--
    }
}

Using a labeled continue in a loop

A labeled continue statement terminates execution of the iteration and transfers control to the targeted enclosing iteration or switch statement label.

In the following example, the innermost for is terminated when $condition is True and iteration continues with the second for loop at labelB.

:labelA for ($i = 1; $i -le 10; $i++) {
    :labelB for ($j = 1; $j -le 10; $j++) {
        :labelC for ($k = 1; $k -le 10; $k++) {
            if ($condition) {
                continue labelB
            } else {
                $condition = Update-Condition
            }
        }
    }
}

Using continue in a switch statement

An unlabeled continue statement within a switch terminates execution of the current switch iteration and transfers control to the top of the switch to get the next input item.

When there is a single input item continue exits the entire switch statement. When the switch input is a collection, the switch tests each element of the collection. The continue exits the current iteration and the switch continues with the next element.

switch (1,2,3) {
  2 { continue }  # moves on to the next element, 3
  default { $_ }
}

1
3

Using continue in a trap statement

If the final statement executed in the body a trap statement is continue, the trapped error is silently ignored and execution continues with the statement immediately following the one that caused trap to occur.

Do not use continue outside of a loop, switch, or trap

When continue is used outside of a construct that directly supports it (loops, switch, trap), PowerShell looks up the call stack for an enclosing construct. If it can't find an enclosing construct, the current runspace is quietly terminated.

This means that functions and scripts that inadvertently use a continue outside of an enclosing construct that supports it, can inadvertently terminate their callers.

Using continue inside a pipeline, such as a ForEach-Object script block, not only exits the pipeline, it potentially terminates the entire runspace.

Jaa