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POPowershell scripting: recommended way to implement ShouldProcess when function calls are nested?
 

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  1. POPowershell scripting: recommended way to implement ShouldProcess when function calls are nested?
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    <p>Test script:</p> <pre><code>function outer { [cmdletbinding(supportsshouldprocess=$true)] param($s) process { $pscmdlet.shouldprocess("outer $s", "ShouldProcess") | out-null "" | out-file "outer $s" inner ImplicitPassthru inner VerbosePassthru -Verbose:$Verbose inner WhatifPassthru -WhatIf:$WhatIf } } function inner { [cmdletbinding(supportsshouldprocess=$true)] param($s) process { $pscmdlet.shouldprocess("inner $s", "ShouldProcess") | out-null "" | out-file "inner $s" } } "`n** NORMAL **" outer normal "`n** VERBOSE **" outer verbose -Verbose "`n** WHATIF **" outer whatif -WhatIf </code></pre> <p>Output:</p> <pre><code>** NORMAL ** VERBOSE: Performing operation "ShouldProcess" on Target "inner VerbosePassthru". What if: Performing operation "ShouldProcess" on Target "inner WhatifPassthru". What if: Performing operation "Output to File" on Target "inner WhatifPassthru". ** VERBOSE ** VERBOSE: Performing operation "ShouldProcess" on Target "outer verbose". VERBOSE: Performing operation "ShouldProcess" on Target "inner VerbosePassthru". What if: Performing operation "ShouldProcess" on Target "inner WhatifPassthru". What if: Performing operation "Output to File" on Target "inner WhatifPassthru". ** WHATIF ** What if: Performing operation "ShouldProcess" on Target "outer whatif". What if: Performing operation "Output to File" on Target "outer whatif". What if: Performing operation "ShouldProcess" on Target "inner ImplicitPassthru". What if: Performing operation "Output to File" on Target "inner ImplicitPassthru". What if: Performing operation "ShouldProcess" on Target "inner VerbosePassthru". What if: Performing operation "Output to File" on Target "inner VerbosePassthru". What if: Performing operation "ShouldProcess" on Target "inner WhatifPassthru". What if: Performing operation "Output to File" on Target "inner WhatifPassthru". </code></pre> <p>To my eye there are several oddities here:</p> <ul> <li>Specifying -WhatIf:$foo will <strong>always</strong> turn on $WhatIf in the callee (and its callees), no matter what $foo is.</li> <li>When you do specify -WhatIf "for real" (without constraining it to an existing variable), it propagates to callees implicitly. No need for passthru or splatting.</li> <li>Unlike -WhatIf, explicit -Verbose does not cascade to callees implicitly.</li> <li>When you try to manually passthru -Verbose:$foo, you do see behavior is similar to -WhatIf:$foo. But it only affects scripts that manually test $psCmdlet.ShouldProcess() -- built in cmdlets aren't affected.</li> </ul> <p><strong><em>N.B.</strong>: Confirm behaves identical to WhatIf. I omitted it for brevity.</em></p> <p>Searching the web and Connect, I see hardly any in-depth discussion of ShouldProcess behavior (pro or con) as pertains to advanced functions. Closest thing is <a href="http://blogs.technet.com/jamesone/archive/2009/12/22/powershell-parameters-2-common-parameters.aspx" rel="noreferrer">a post from James O'Neill</a> that recommends passing a single instance of $psCmdlet throughout the call stack. However, he does so to workaround an entirely different problem (avoiding multiple -Confirm prompts). Meanwhile, when you stick with the standard $psCmdlet provided to each function, I see no docs on what to expect...much less design patterns, best practices, etc...</p>
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