Inject custom steps in a PowerShell script

Question

Assume I have the following PS Script myscript.ps1:

param(
  [string]$ID
)

Write-Host "Step 1 $ID"
Write-Host "Step 2 $ID"
# Inject some custom step here
Write-Host "Step 3 $ID"

That I call from another PS script with

$ [path]\myscript.ps1 -ID 001
$ [path]\myscript.ps1 -ID 002
$ [path]\myscript.ps1 -ID 003

Now when I run the last call:

$ [path]\myscript.ps1 -ID 003

I would like to trigger some custom behavior/steps just after:

Write-Host "Step 2 $ID"

in myscript.ps1. I considered this:

$ [path]\myscript.ps1 -ID 001
$ [path]\myscript.ps1 -ID 002
$ [path]\myscript.ps1 -ID 003 -customScript "[path]\custom.ps1"

and then update myscript.ps1 to:

param(
  [string]$ID,
  [string]$custom=""
)

Write-Host "Step 1 $ID"
Write-Host "Step 2 $ID"
if($custom) {
    & $custom
}
# Inject some custom step here
Write-Host "Step 3 $ID"

Maybe there are some more elegant way of doing this?

I have looked at: http://blogs.msdn.com/b/powershell/archive/2008/06/11/powershell-eventing-quickstart.aspx

but it does not really seem to fit the purpose.

beatcracker · Accepted Answer · 2015-12-08 13:39:58Z

4

You can pass custom ScriptBlock and execute it:

param(
  [string]$ID,
  [scriptblock]$custom
)

Write-Host "Step 1 $ID"
Write-Host "Step 2 $ID"

# Inject some custom step here
if($custom){. $custom}

Write-Host "Step 3 $ID"

Example:

$ [path]\myscript.ps1 -ID 001
$ [path]\myscript.ps1 -ID 002
$ [path]\myscript.ps1 -ID 003 -custom {Write-Host "I'm a custom scriptblock!"}

More about executing scriptblocks:

Some observations about Powershell script blocks.

edited Dec 8, 2015 at 13:39

answered Dec 8, 2015 at 13:32

beatcracker

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4 Comments

Ansgar Wiechers Over a year ago

Whether that's more elegant than passing the path to a custom script file is debatable, though.

beatcracker Over a year ago

@AnsgarWiechers Scriptblock can run custom scipt, so it's more versatile IMO.

Ansgar Wiechers Over a year ago

A custom script can run custom scriptblock as well. Both approaches are equivelent in terms of functionality.

beatcracker Over a year ago

@AnsgarWiechers Scriptblocks are easier to build on the fly then files. Saves you one intermediate step and disk I/O. Of course, it depends on a amount of code to execute - after some threshold creating a full-fledged script is more preferable. But for the short snippets I'd use a scriptblock.

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