about_For

Article
09/19/2022

Short description

Describes a language command you can use to run statements based on a conditional test.

Long description

The For statement (also known as a For loop) is a language construct you can use to create a loop that runs commands in a command block while a specified condition evaluates to $true.

A typical use of the For loop is to iterate an array of values and to operate on a subset of these values. In most cases, if you want to iterate all the values in an array, consider using a Foreach statement.

Syntax

The following shows the For statement syntax.

for (<Init>; <Condition>; <Repeat>)
{
    <Statement list>
}

The Init placeholder represents one or more commands that are run before the loop begins. You typically use the Init portion of the statement to create and initialize a variable with a starting value.

This variable will then be the basis for the condition to be tested in the next portion of the For statement.

The Condition placeholder represents the portion of the For statement that resolves to a $true or $false Boolean value. PowerShell evaluates the condition each time the For loop runs. If the statement is $true, the commands in the command block run, and the statement is evaluated again. If the condition is still $true, the commands in the Statement list run again. The loop is repeated until the condition becomes $false.

The Repeat placeholder represents one or more commands, separated by commas, that are executed each time the loop repeats. Typically, this is used to modify a variable that is tested inside the Condition part of the statement.

The Statement list placeholder represents a set of one or more commands that are run each time the loop is entered or repeated. The contents of the Statement list are surrounded by braces.

Support for multiple operations

The following syntaxes are supported for multiple assignment operations in the Init statement:

# Comma separated assignment expressions enclosed in parenthesis.
for (($i = 0), ($j = 0); $i -lt 10; $i++)
{
    "`$i:$i"
    "`$j:$j"
}

# Sub-expression using the semicolon to separate statements.
for ($($i = 0;$j = 0); $i -lt 10; $i++)
{
    "`$i:$i"
    "`$j:$j"
}

The following syntaxes are supported for multiple assignment operations in the Repeat statement:

# Comma separated assignment expressions.
for (($i = 0), ($j = 0); $i -lt 10; $i++, $j++)
{
    "`$i:$i"
    "`$j:$j"
}

# Comma separated assignment expressions enclosed in parenthesis.
for (($i = 0), ($j = 0); $i -lt 10; ($i++), ($j++))
{
    "`$i:$i"
    "`$j:$j"
}

# Sub-expression using the semicolon to separate statements.
for ($($i = 0;$j = 0); $i -lt 10; $($i++;$j++))
{
    "`$i:$i"
    "`$j:$j"
}

Note

Operations other than pre or post increment may not work with all syntaxes.

For multiple Conditions use logical operators as demonstrated by the following example.

for (($i = 0), ($j = 0); $i -lt 10 -and $j -lt 10; $i++,$j++)
{
    "`$i:$i"
    "`$j:$j"
}

For more information, see about_Logical_Operators.

Examples

At a minimum, a For statement requires the parenthesis surrounding the Init, Condition, and Repeat part of the statement and a command surrounded by braces in the Statement list part of the statement.

Note that the upcoming examples intentionally show code outside the For statement. In later examples, code is integrated into the For statement.

For example, the following For statement continually displays the value of the $i variable until you manually break out of the command by pressing CTRL+C.

$i = 1
for (;;)
{
    Write-Host $i
}

You can add additional commands to the statement list so that the value of $i is incremented by 1 each time the loop is run, as the following example shows.

for (;;)
{
    $i++; Write-Host $i
}

Until you break out of the command by pressing CTRL+C, this statement will continually display the value of the $i variable as it is incremented by 1 each time the loop is run.

Rather than change the value of the variable in the statement list part of the For statement, you can use the Repeat portion of the For statement instead, as follows.

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

This statement will still repeat indefinitely until you break out of the command by pressing CTRL+C.

You can terminate the For loop using a condition. You can place a condition using the Condition portion of the For statement. The For loop terminates when the condition evaluates to $false.

In the following example, the For loop runs while the value of $i is less than or equal to 10.

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

Instead of creating and initializing the variable outside the For statement, you can perform this task inside the For loop by using the Init portion of the For statement.

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

You can use carriage returns instead of semicolons to delimit the Init, Condition, and Repeat portions of the For statement. The following example shows a For that uses this alternative syntax.

for ($i = 0
  $i -lt 10
  $i++){
  $i
}

This alternative form of the For statement works in PowerShell script files and at the PowerShell command prompt. However, it is easier to use the For statement syntax with semicolons when you enter interactive commands at the command prompt.

The For loop is more flexible than the Foreach loop because it allows you to increment values in an array or collection by using patterns. In the following example, the $i variable is incremented by 2 in the Repeat portion of the For statement.

for ($i = 0; $i -le 20; $i += 2)
{
    Write-Host $i
}

The For loop can also be written on one line as in the following example.

for ($i = 0; $i -lt 10; $i++) { Write-Host $i }