Conditionals

Conditionals enable execution of code based on provided conditions. They take in an expression and check if it is True or False. If the expression is True, one set of statements is executed. Otherwise, another set of instructions is performed. This control of flow makes programs more robust by enabling them to address multiple scenarios.

There are four types of conditional statements in PowerShell:

1. if
2. else
3. elseif
4. switch

if

The if statement executes a block of code if the condition expression is True.

$my_num = 2
if($my_num -eq 2){
  Write-Host "A True Statement"
}
Write-Host "After the if statement"

The example above prints "A True Statement" and "After the if statement" if $my_num is equal to 2. Otherwise, it skips the statement within the if curly braces { } and just prints "After the if statement".

else

The else clause always follows the if statement.

• If the condition is True, the code in the if section is executed.
• If the condition is False, the code in the else section is executed.

$my_num = 2
if($my_num -gt 0) {
  # Prints if $my_num is more than 0
  Write-Host "A positive number"
}
else {
  # Prints if $my_num is less than or equal to 0
  Write-Host "A negative number"
}

elseif

One or more elseif statements can be added between if and else to test multiple conditions.

$my_num = 2
if($my_num -gt 0) {
  # Prints if $my_num is more than 0
  Write-Host "A positive number"
}
elseif ($my_num -lt 0) {
  # Prints if $my_num is less than 0
  Write-Host "A negative number"
}
else {
  # Prints if both of the previous conditions fail
  Write-Host "Zero"
}

switch

The switch statement provides a simpler syntax for the same behavior as if / elseif expressions that check for equality.

$my_num = 2
switch ($my_num) {
  1 {
    Write-Host "You chose 1"
  }
  2 {
    Write-Host "You chose 2"
  }
  3 {
    Write-Host "You chose 3"
  }
  default {
    Write-Host "No match"
  }
}

The example above prints "You chose 2". If $my_num was 4, for example, it would print "No match" since the default clause is run if all other conditions fail.

PowerShell allows conditional expressions to be used in switch statements.

$my_num = 10
switch ($my_num) {
  {$PSItem -gt 5} {
    Write-Host "Greater than 5"
  }
  {$PSItem -gt 0} {
    Write-Host "Greater than 0"
  }
  {$PSItem -lt 5} {
    Write-Host "Less than 5"
  }
}

Note: $PSItem is an automatic variable that contains the value passed to the switch statement. It can be replaced with its shorthand alias $_.

The above example prints "Greater than 5" and "Greater than 0" since their corresponding conditions are True. Even if a condition is True, the following conditions are still tested unless a break statement is provided, as in the example below which only prints "Greater than 5".

$my_num = 10
switch ($my_num) {
  {$_ -gt 5} {
    Write-Host "Greater than 5"
    break
  }
  {$_ -gt 0} {
    Write-Host "Greater than 0"
  }
  {$_ -lt 5} {
    Write-Host "Less than 5"
  }
}