Block Retry using Powershell

I’ve been doing a lot of Powershell scripting lately, and one of the features I’ve really been pining for is the ability to apply some form of retry logic to either a function or a block.

Take the following sample:

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function RandomlyFail
{
    $rnd = Get-Random -minimum 1 -maximum 3
    if ($rnd -eq 2) {
        throw "OH NOES!!!"
    }
    $Host.UI.WriteLine("W00t!!!")
}

Depending on what the random number we get is, we’ll get one of two scenarios:

# Success
RandomlyFail

W00t!!!

# Failure
RandomlyFail

OH NOES!!!
At line:62 char:9
+         throw "OH NOES!!!"
+         ~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : OperationStopped: (OH NOES!!!:String) [], RuntimeException
    + FullyQualifiedErrorId : OH NOES!!!

Now, if this happened to be part of a larger script and we didn’t have everything wrapped in a try..catch block, execution could potentially stop there.

Since Powershell supports closures, we can write a function that accepts a script block as a parameter.

Now, if we retrofit our sample above:

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Execute-With-Retry -RetryDelay 1 -VerboseOutput $true { RandomlyFail }
Failed to execute [ RandomlyFail ]: OH NOES!!!
DEBUG: Waiting 1 second(s) before attempt #1 of [ RandomlyFail ]
Failed to execute [ RandomlyFail ]: OH NOES!!!
DEBUG: Waiting 1 second(s) before attempt #2 of [ RandomlyFail ]
Failed to execute [ RandomlyFail ]: OH NOES!!!
DEBUG: Waiting 1 second(s) before attempt #3 of [ RandomlyFail ]
Failed to execute [ RandomlyFail ]: OH NOES!!!
DEBUG: Waiting 1 second(s) before attempt #4 of [ RandomlyFail ]
W00t!!!
DEBUG: Successfully executed [ RandomlyFail ]

The inspiration for this comes from an excellent article by Pawel Pabich.

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