Can I pipe into a switch statement stored in a variable? - powershell

Question

I have a variable that stores a switch statement
$com = '
switch ($_)
{
1 {"It is one."}
2 {"It is two."}
3 {"It is three."}
4 {"It is four."}
}
'
I am trying to pipe in the number to run the switch statement
something like:
1 | iex($com)

Answer 1

Your options are:
A scriptblock or function with a process block:
$com = {
process {
switch ($_) {
1 { "one." }
2 { "two." }
3 { "three." }
}
}
}
function thing {
process {
switch ($_) {
1 { "one." }
2 { "two." }
3 { "three." }
}
}
}
1..3 | & $com
1..3 | thing
A filter, exactly the same functionality:
filter thing {
switch ($_) {
1 { "one." }
2 { "two." }
3 { "three." }
}
}
1..3 | thing
Using ScriptBlock.Create method (this would require a process block in the string expression):
$com = '
process {
switch ($_) {
1 { "one." }
2 { "two." }
3 { "three." }
}
}
'
1..3 | & ([scriptblock]::Create($com))
Using ScriptBlock.InvokeWithContext method and the automatic variable $input, this technique does not stream and also requires an outer scriptblock to work, it's just to showcase and should be discarded as an option:
$com = '
switch ($_) {
1 { "one." }
2 { "two." }
3 { "three." }
}
'
1..3 | & { [scriptblock]::Create($com).InvokeWithContext($null, [psvariable]::new('_', $input)) }
Using Invoke-Expression, also requires an outer scriptblock with a process block (should be discarded - from all techniques displayed above this is the worst one, the string expression is being evaluated per item passed through the pipeline):
$com = '
switch ($_) {
1 { "one." }
2 { "two." }
3 { "three." }
}
'
1..3 | & { process { Invoke-Expression $com } }