The 411 on Powershell Operators – Part 1 the -eq operator

Holy Schnikees there are a lot of operators in Powershell! This may not be an exact count  but looking through the help file it looks like there are 57 operators!  I am using the CTP – Powershell V2 –  which introduced a handful of new operators, particularly  -join and -split.

I’d like to start a series on some of the operators and how they can be used. I’d like to start with the most basic of operators, the -eq operator. This is the equality operator.

Note that this is different than the assignment operator “=” which is used to assign values to variables.

In a lot of programming languages, the “==” operator is used for equality.  Here’s a quick example.

   1: PS C:\Users\andys> 1 -eq 1

   2: True

   3: PS C:\Users\andys> 2 -eq 3

   4: False

This is pretty normal, (and boring). Do notice that this returns the boolean value True.

But what about if we compare an array  to an integer.

   1: PS C:\Users\andys> function new-array {,$args}

   2: PS C:\Users\andys> $i = new-array 1 2 3 4 5

   3: PS C:\Users\andys> $i

   4: 1

   5: 2

   6: 3

   7: 4

   8: 5

   9: PS C:\Users\andys> $i -eq 3

  10: 3

Interesting that the value that is returned is the value of the item in the array that was a match. It was NOT a boolean. You can read about my new-array function here for more info, but it allows you to create an array with a lot less typing.

The same is true with strings.

   1: PS C:\Users\andys> $s = new-array one two cat dog

   2: PS C:\Users\andys> $s -eq "cat"

   3: cat

   4: PS C:\Users\andys> $s -eq "not-here"

   5: PS C:\Users\andys>

However, if we use this in an if statement, it will get converted to a boolean value.

   1: PS C:\Users\andys> if ($s -eq "cat") {return $true} else {return $false}

   2: True

   3: PS C:\Users\andys> if ($s -eq "no") {return $true} else {return $false}

   4: False

   5: PS C:\Users\andys>

We can use an implicit cast to show this:

   1: PS C:\Users\andys> [bool]($s -eq "cat")

   2: True

   3: PS C:\Users\andys> [bool]($s -eq "not here")

   4: False

   5: PS C:\Users\andys>

I am continuously amazed at how deep you can go with exploring Powershell and looking at subtle nuances such as these. It’s really pretty awesome to think about how all these operators just work as you expect, given the context you are using them in.

 

Andy

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