The simplest way to retry in PowerShell

$attempt = 0
do {
    try {
        # Do something that has a high possiblity to crash.
        ping a

        if (-not $LASTEXITCODE) {
             $success = $true
        } else {
            throw "Transient error. LASTEXITCODE is $LASTEXITCODE."
        }
    }
    catch {
        if ($attempt -eq 5) {
            # You can do some extra logging here.
            Write-Error "Task failed. With all $attempt attempts. Error: $($Error[0])"
            throw
        }

        Write-Host "Task failed. Attempt $attempt. Will retry in next $(5 * $attempt) seconds. Error: $($Error[0])" -ForegroundColor Yellow
        Start-Sleep -Seconds $(5 * $attempt)
    }
    
    $attempt++
    
} until($success)

Running sample:

Failed:

PS C:\\Users\\AnduinXue\\Desktop> .\\test.ps1  
Ping request could not find host a. Please check the name and try again.  
Task failed. Attempt 0. Will retry in next 0 seconds. Error: Transient error. LASTEXITCODE is 1.  
Ping request could not find host a. Please check the name and try again.  
Task failed. Attempt 1. Will retry in next 5 seconds. Error: Transient error. LASTEXITCODE is 1.  
Ping request could not find host a. Please check the name and try again.  
Task failed. Attempt 2. Will retry in next 10 seconds. Error: Transient error. LASTEXITCODE is 1.  
Ping request could not find host a. Please check the name and try again.  
Task failed. Attempt 3. Will retry in next 15 seconds. Error: Transient error. LASTEXITCODE is 1.  
Ping request could not find host a. Please check the name and try again.  
Task failed. Attempt 4. Will retry in next 20 seconds. Error: Transient error. LASTEXITCODE is 1.  
Ping request could not find host a. Please check the name and try again.  
C:\\Users\\AnduinXue\\Desktop\\test.ps1 : Task failed. With all 5 attempts. Error: Transient error. LASTEXITCODE is 1.  
At line:1 char:1  
\+ .\\test.ps1  
\+ ~~~~~~~~~~  
    + CategoryInfo          : NotSpecified: (:) \[Write-Error\], WriteErrorException  
    + FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,test.ps1  
  
Transient error. LASTEXITCODE is 1.  
At C:\\Users\\AnduinXue\\Desktop\\test.ps1:10 char:13  
\+             throw "Transient error. LASTEXITCODE is $LASTEXITCODE."  
\+             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
    + CategoryInfo          : OperationStopped: (Transient error. LASTEXITCODE is 1.:String) \[\], RuntimeException  
    + FullyQualifiedErrorId : Transient error. LASTEXITCODE is 1.

Success one:

PS C:\\Users\\AnduinXue\\Desktop> .\\test.ps1  
  
Pinging www.a.shifen.com \[112.80.248.75\] with 32 bytes of data:  
Reply from 112.80.248.75: bytes=32 time=8ms TTL=56  
Reply from 112.80.248.75: bytes=32 time=8ms TTL=56  
Reply from 112.80.248.75: bytes=32 time=8ms TTL=56  
Reply from 112.80.248.75: bytes=32 time=9ms TTL=56  
  
Ping statistics for 112.80.248.75:  
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),  
Approximate round trip times in milli-seconds:  
    Minimum = 8ms, Maximum = 9ms, Average = 8ms

GPT-4

I just finished reading your blog post on implementing a retry mechanism in PowerShell. I find the content very useful, and I appreciate the simplicity of the approach you've presented. The core idea of using a loop to retry a potentially failing operation is a great way to ensure the task's completion without manual intervention.

The example you have provided, which uses the "ping" command, is a good illustration of a transient error that might benefit from a retry mechanism. I particularly like how you have used the $LASTEXITCODE variable to check for success or failure and the Start-Sleep command to introduce a delay between retries. This makes the script more resilient and adaptable to different situations.

However, I noticed a small issue in your script. The Start-Sleep -Seconds $(5 * $attempt) command might cause an excessive delay in later retries, as it increases the waiting time exponentially. Instead, you could consider using a fixed delay between retries or using an incremental delay (e.g., 5 seconds for the first retry, 10 seconds for the second, etc.) to avoid excessive waiting times.

In conclusion, your blog post provides a valuable and straightforward solution for implementing a retry mechanism in PowerShell. With some minor adjustments to the waiting time between retries, this script could become even more efficient and useful. Keep up the great work, and I look forward to reading more of your insightful blog posts in the future.

Anduin's Tech Blog