The complete function definition syntax for a function in PowerShell that will have a Cmdlet-like behavior is as follows:
function ( )
{
begin {
}
process {
}
end {
}
}
To illustrate how the processing occurs, here is a sample function named MockCmdlet:
function MockCmdlet ($val)
{
begin {
$count = 0;
Write-Host "( begin) : Count = $count; val = $val";
}
process {
$count++;
Write-Host "(process) : Count = $count; val = $val; `$_ = $_";
}
end {
Write-Host "( end) : Count = $count; val = $val";
}
}
This function takes as input a variable $val. In the begin block, the counter variable $count is initialized to 0 and the values of the $count and $val variables are written to the console. In the process block, the $count variable in incremented and the previous two values along with the value of the current pipeline value stored in $_ is written to the console. And finally, in the end block, the values of $count and $val are written again.
The following example usage illustrates how the processing of each of these blocks occur. In this example, I pass in an array of size three with the values 1, 2, and 3 through the pipeline while supplying the value of 5 in the function parameter list. You'll see that the begin block is processed once, the process block is processed once for each value in the pipeline, and the end block is processed once.
PS> 1, 2, 3 | MockCmdlet 5
( begin) : Count = 0; val = 5
(process) : Count = 1; val = 5; $_ = 1
(process) : Count = 2; val = 5; $_ = 2
(process) : Count = 3; val = 5; $_ = 3
( end) : Count = 3; val = 5
So, if you find yourself wishing you had initialization and termination behavior in your script functions you'll now have the tools you need to make your own function with Cmdlet type behavior.