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ABOUT FOR
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; $i++)
{
"`$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 }
SEE ALSO
about_Comparison_Operators
about_Foreach