Matching a string against a list of predefined strings

Published on: 4th Dec 2019

Updated on: 16th Jan 2022

Explanation

To match an input string against a single pattern, you may use the -LIKE operator just like SQL SELECT statement.

if ($my_string -like "*helo*") {
    # do something here
}

Whereas to match an input string against a list of predefined strings, we use -MATCH parameter. To show you how this works, we wrote a function that will check whether the input string is matching the weekday in the predefined format.

Our weekday format:

"_" + "first 3 character of weekday text"

So, our function will look like this (you may copy the script below into a ps1 file and execute it):

# returns true if the weekday param is matching the predefined file name convention.
function Is-weekday() {
    param (
        [string]$wd
    )

    if ($wd -match "_mon|_tue|_wed|_thu|_fri|_sat|_sun") {
        return $true
    }

    return $false
}

# To test if it works, run the following line:

$weekday = "_wed"
Is-weekday $weekday
# result on screen: True

# Let's say we remove the underscore symbol from $weekday, we will get False as the result.
$weekday = "wed"
Is-weekday $weekday# result on screen:  False

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Author

Lau Hon Wan, software developer.