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10) WinDiff

Windows PowerShell - Conditional Operators

Introduction to PowerShell Conditional Operators

I think of PowerShell's conditional operators as filters.  Perhaps you are suffering from a common problem - too much information?  If so, then choosing the most suitable PowerShell operator: -match, -like or -contains will help you to distil the key information.

Introduction to: -match  -like and -contains.

-Match -like and -contains are all similar PowerShell conditional operators, yet each has a subtle specialization.  My advice is keep experimenting until you find the particular conditional operator that suits your circumstance. Have faith that you will be able to manipulate one of this trio, and thus achieve the degree of pattern matching that you seek. 

Topics for PowerShell's Conditional Operators

• Example 1 -Match
• Example 2 -Like
• Example 3 -Contains
• Summary of Conditional Operators

Also note, these operators are in addition to the ubiquitous comparison operators, -eq, 'If' and 'elseif'.

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Example 1 -Match Conditional Operator

The 'match' can be anywhere in the string.  Moreover, the pattern does not have to be a complete, and this is the biggest benefit of match.  -Match uses regular expressions for pattern matching.  Incidentally -match, and the other PowerShell conditional operators, all have a negative form, for example -notmatch.

Example 1a - Match does not have to be at the beginning

Example 1b - Naturally a completely wrong name is no good

Example 1c - Wrong date

Example 1d - Wildcard?  Rides to the rescue

Example 1e - WmiObject and Where, using * as a Wildcard

Here is a real-life -match example using WmiObject and a where clause, observer the Wildcard*.

Additional PowerShell Character Classes

A character class is a broader form of wildcard, which represents an entire group of characters.  You can use these for really wide-ranging searches.  PowerShell recognizes the following character classes:

\w matches any word character, meaning letters and numbers.
\s matches any white space character, such as tabs, spaces, and so forth.
\d matches any digit character.

There are also the reverse or negative versions which employ a capital letter.  (Can be hard to get a false with these!)

\W (capital W) any non-word character
\S any non-white space.
\D any non digit. 

Negative -notmatch

For negative conditions, there is an alternative form called -notmatch.  PowerShell also has ErrorAction silentlyContinue.

Example 2 -Like Conditional Operator

With -like, both sides of the expression have to be the same, fortunately, you can employ the usual wildcards * and ?

Example 2a - Having only part of the string is no good for -like

Example 2b - Just the start of the string not enough

Example 2c - Wildcard * is useful for -like

Example 2d - Wildcard*  but the rest has to be correct

Example 2e - * Wildcards *  Double wildcards are handy

If your logic needs the negative, then try -notlike.  In addition,-like -and -notlike have variants that force case sensitivity. -clike and -cnotlike. 

Difference Between -like and -match

Example 3 -Contains Conditional Operator

The conditional operator -contains is similar to -eq, except it returns 'True' or 'False'.  -contains is designed for situations where you have a collection and wish to test one particular item.

Example 3a - Checks each item between the commas

Example 3b  -Contains requires exact equality

Example 3c - Wildcards are a waste of time with -contains

About_Comparison_Operators

Summary of PowerShell Conditional Operators

So often we suffer from information overload. Working with PowerShell is no different, however it does supply three conditional operators to filter your information: -match, -like and –contains.  Each operator has different properties; with research, you can get just the filter you need, and thus filter the desired stream of information into your script’s output.

See more Windows PowerShell examples

• PowerShell Home  • If Statement  • Conditional Operators  • Switch  • Loops  • Brackets

• Comparison operators  • -Match  • Where Filter

Please write in if you have a better example script. Also please report any factual mistakes, grammatical errors or broken links, I will be happy to correct the fault.

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