The Conditional If does not produce error if specific syntax is incorrect

Steps to reproduce:

Using the conditional If, use the incorrect comparison operator of = instead of -eq:

$Sky = 'blue'

if ($Sky = 'green') {

    Write-Host "The sky is green"
}

Expected behavior

We should get the error Unexpected token '=' in expression or statement like this if we used the incorrect comparison operator equals:

ParserError: 
Line |
   3 |  if ($Sky equals 'green') {
     |           ~~~~~~
     | Unexpected token 'equals' in expression or statement.

The variable should also not have been changed to green as you don’t set variables inside of the condition to be met inside of conditionals.

Actual behavior

No error is produced, the script continues, and the variable is set to green

## Environment data

Observed in both PowerShell & Windows PowerShell

[vexx32]

This is by design.

What’s happening here is that the expression $sky = 'green', which doesn’t normally output data, can also be written ($sky = 'green'), which does produce output (it outputs the value 'green' to the pipeline as well as storing it in the variable).

Knowing this, the parentheses in an if statement (and indeed other conditionals like switch) behave the same way, forcing the output and processing it in the conditional statement.

C# works the same way, it’s likely a pattern copied from there.

$sky = 'green' # no output
($sky = 'blue') # outputs 'blue'
if ($sky = 'green') {
    # 'green' is evaluated by the if statement and coerces to a boolean `$true` as it is not an empty or null string.
    Write-Warning "we do indeed get here"
}

$sky # is now 'green'

In other words, assigning a variable in an if statement will always be an assignment and a test of the value you assigned, and never a test of the current value of the variable.

[user8446]

Thank you @vexx32