In looking at entries in this year's Scripting Games, as well as posts I see in PowerShell forums, I thought I'd post a short guide to properly using Try\/Catch. This is the way I think it should be used. Let's start with a Try\/Catch block that might look ok.<\/p>\n
Catch { You would expect that if the service FOO can't be found that the code in the Catch script block will run.<\/p>\n Nope. I got an exception, but my code in the Catch script block did not run. You can only catch terminating exceptions. In order for my Try\/Catch to work properly, I have to make sure that if there is an exception it gets treated as a terminating exception. The best way is to use the common -ErrorAction parameter and set it to Stop.<\/p>\n Catch { The parameter has an alias of -ea which you'll often see used. Now let's see what happens:<\/p>\n That's what I was expecting. Now for the tricky part. Look at this variation.<\/p>\n Catch { What happens when I run this?<\/p>\n How about that? Even without -erroraction, my catch code still ran. Based on this I can safely deduce that the remote connection failure created a terminating exception. But without a lot of trial and error I think it is impossible to know in advance what type of error will throw a terminating exception and what won't. Personally, I think the best thing is to always use -ErrorAction stop on a cmdlet in a Try scriptblock to guarantee you will always get a terminating exception.<\/p>\n","protected":false},"excerpt":{"rendered":" In looking at entries in this year’s Scripting Games, as well as posts I see in PowerShell forums, I thought I’d post a short guide to properly using Try\/Catch. This is the way I think it should be used. Let’s start with a Try\/Catch block that might look ok. Try { Get-Service Foo } Catch…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[4,8],"tags":[370,534,540,227],"class_list":["post-2175","post","type-post","status-publish","format-standard","hentry","category-powershell","category-scripting","tag-errorhandling","tag-powershell","tag-scripting","tag-trycatch"],"yoast_head":"\n
\nTry {
\n Get-Service Foo
\n}<\/p>\n
\n Write-Warning \"Oops\"
\n Write-Warning $_.Exception.Message
\n}
\n<\/code><\/p>\n
\nPS C:\\work> .\\trydemo.ps1
\nGet-Service : Cannot find any service with service name 'Foo'.
\nAt C:\\work\\trydemo.ps1:4 char:14
\n+ Get-Service <<<< Foo\n + CategoryInfo : ObjectNotFound: (Foo:String) [Get-Service], Serv\n iceCommandException\n + FullyQualifiedErrorId : NoServiceFoundForGivenName,Microsoft.PowerShell.\n Commands.GetServiceCommand\n<\/code><\/p>\n
\nTry {
\n Get-Service Foo -ErrorAction Stop
\n}<\/p>\n
\n Write-Warning \"Oops\"
\n Write-Warning $_.Exception.Message
\n}
\n<\/code><\/p>\n
\nPS C:\\work> .\\trydemo.ps1
\nWARNING: Oops
\nWARNING: Cannot find any service with service name 'Foo'.
\nPS C:\\work>
\n<\/code><\/p>\n
\nTry {
\n Get-Service -ComputerName Bogus
\n}<\/p>\n
\n Write-Warning \"Oops\"
\n Write-Warning $_.Exception.Message
\n}
\n<\/code><\/p>\n
\nPS C:\\work> .\\trydemo.ps1
\nWARNING: Oops
\nWARNING: Cannot open Service Control Manager on computer 'Bogus'. This
\noperation might require other privileges.
\n<\/code><\/p>\n