#PowershellBasics: Setting a variable vs a comparison.

In SQL Server both the set and equality functions are handled by the equals sign (=). For example:

Set

SET @var = 5;
SELECT @var = 5;

Equality

SELECT CASE WHEN @var = 5 THEN 'Equals' ELSE 'Not Equals' END;
IF @var = 5
PRINT 'Equals';
ELSE
PRINT 'Not Equals';

However, in some other languages that’s not how it works. In PowerShell for example the equals sign is always a set operation. In order to do a comparison you have to use -eq for equals or -ne for not equals. If you aren’t expecting it this can cause rather odd results

$var = 3
IF ($var = 5) {
    Write-Host "Equals"
} ELSE {
    Write-Host "Not Equals"
} 

I’ll bet you expect the output of that code snippit to be Not Equals right? It’s certainly what I was expecting the other day. But nope. It’s always going to be Equals. Why? If we change it slightly it becomes pretty obvious.

$var = 3
IF ($var = 5) {
    Write-Host $var
}

The result of this code snippit is 5. The reason is simple. Like I said above, the equals sign is always (at least to the best of my knowledge) a set operation. If we want to this to work correctly we have to use -eq.

$var = 3
IF ($var -eq 5) {
Write-Host "Equals"
} ELSE {
Write-Host "Not Equals"
}

If you want to look at other comparison operators for PowerShell you can look here.