Catching dynamic exception types in PowerShell -

i'm working on powershell library automates network management operations. of these operations have arbitrary delays, , each can fail in unique ways. handle these delays gracefully, i'm creating generic retry function has 3 main purposes:

1. execute arbitrary command (with parameters)
2. if fails in recognized way, try again, limit
3. if fails in unexpected way, bail , report

the problem item #2. want able specify expected exception type command. how can in powershell?

here's function:

function retry-command {     [cmdletbinding()]     param(         [parameter(mandatory=$true, position=0)]         [string] $name,          [parameter(mandatory=$true, position=1)]         [string] $scriptblock,          [string[]] $argumentlist,         [int] $maxattempts=3,         [int] $retryseconds=10,         [system.exception] $retryexception=[system.management.automation.runtimeexception]     )     $attempts = 1     $keeptrying = $true     $cmd = [scriptblock]::create($scriptblock)     {         try {             &$cmd @argumentlist             $keeptrying = $false             write-verbose "command [$commandname] succeeded after $attmpts attempts."         } catch [$retryexception] {             $msg = "command [$commandname] failed. attempt $attempts of $maxattempts."             write-verbose $msg;             if ($maxattempts -gt $attempts) {                 write-debug "sleeping $retryseconds"                 start-sleep -seconds $retryseconds             } else {                 $keeptrying = $false                 write-debug "reached $attempts attempts. re-raising exception."                 throw $_.exception             }         } catch [system.exception] {             $keeptrying = $false             $msg = "unexpected exception while executing command [$commandname]: "             write-error $msg + $_.exception.tostring()             throw $_.exception         } {             $attempts += 1         }     } while ($true -eq $keeptrying) } 

i call this:

$result = retry-command -name = "foo bar" -scriptblock $cmd -argumentlist $cmdargs 

but result:

retry-command : cannot process argument transformation on parameter 'retryexception'.  cannot convert "system.management.automation.runtimeexception" value of type "system.runtimetype" type "system.exception". @ foo.ps1:111 char:11 + $result = retry-command <<<<  -name "foo bar" -scriptblock $cmd -argumentlist $cmdargs     + categoryinfo          : invaliddata: (:) [retry-command], parameterbindin...mationexception     + fullyqualifiederrorid : parameterargumenttransformationerror,retry-command 

this seems saying type of [system.management.automation.runtimeexception] not [system.exception], instead [system.runtimetype] makes sense.

so, how specify type of exception caught?

it's not possible use variable catch criteria, has type-object (or something), else gives error. workaround this:

#you can name of exception using following (or .name short name) #ps > $myerr.exception.gettype().fullname #system.unauthorizedaccessexception   function test {     param(     #validate specified name class inherits system.exception base class     [validatescript({[system.exception].isassignablefrom([type]$_)})]     $exceptiontype     )      try {         #test-script, throw unauthorizedaccessexception when not run admin         (get-content c:\test.txt) | % { $_ -replace 'test','lol' } | set-content c:\test.txt     }     catch [system.exception] {         #check if exceptiontype equal value specified in exceptiontype parameter         if($_.exception.gettype() -eq ([type]$exceptiontype)) {             "hello. caught me"         } else {         "uncaught stuff: $($_.exception.gettype())"         }     } } 

a few tests. 1 non-existing type, non-exception type, , working one

ps > test -exceptiontype system.unaut test : cannot validate argument on parameter 'exceptiontype'. cannot convert "system.unaut" val ue of type "system.string" type "system.type". @ line:1 char:21 + test -exceptiontype system.unaut +                     ~~~~~~~~~~~~     + categoryinfo          : invaliddata: (:) [test], parameterbindingvalidationexception     + fullyqualifiederrorid : parameterargumentvalidationerror,test   ps > test -exceptiontype string test : cannot validate argument on parameter 'exceptiontype'. "[system.exception].isassignablef rom([type]$_)" validation script argument value "string" did not return true. determin e why validation script failed , try command again. @ line:1 char:21 + test -exceptiontype string +                     ~~~~~~     + categoryinfo          : invaliddata: (:) [test], parameterbindingvalidationexception     + fullyqualifiederrorid : parameterargumentvalidationerror,test   ps > test -exceptiontype unauthorizedaccessexception hello. caught me