How to change case of back references? - regex

Question

I'm trying to modify a back reference in PowerShell but am having no luck :(
This is my example:
"456,Jane Doe" -replace '^(\d{3}),(.*)$',"| $(`"`$2`".ToUpper()) | `$1 |"
If I run it I get this:
| Jane Doe | 456 |
But I'm really expecting this:
| JANE DOE | 456 |
If I run the following (the same as above but without the '()' on the call to ToUpper):
"456,Jane Doe" -replace '^(\d{3}),(.*)$',"| $(`"`$2`".ToUpper) | `$1 |"
I get this:
| string ToUpper(), string ToUpper(System.Globalization.CultureInfo culture) | 456 |
So it would appear that PowerShell knows that the back reference '$2' is a string but why can't I get PowerShell to convert it to upper case?
Terry

Answer 1

[Regex]::Replace('456,Jane Doe',
'^(\d{3}),(.*)$',
{
param($m)
'| ' + $m.Groups[2].Value.ToUpper() + ' | ' + $m.Groups[1].Value + ' |'
}
)
Not very pretty, I admit. And you sadly cannot use script blocks as replacement in the -replace operator.

Answer 2

Just to explain what is happening, in "| $(`"`$2`".ToUpper()) | `$1 |" PowerShell is evaluating the highlighted subexpression before passing the string to the -replace operator, rather than after the replace operation has occurred.
In other words, ToUpper is called on the string value $2, resulting in | $2 | $1 | being used for the replace operation. You can see this by including a letter in the subexpression string, for example:
"456,Jane Doe" -replace '^(\d{3}),(.*)$',"| $(`"zz `$2`".ToUpper()) | `$1 |"
This has an effective replace string of | ZZ $2 | $1 |, giving | ZZ Jane Doe | 456 | as the result.
Similarly, the second version omitting parenthesis, "| $(`"`$2`".ToUpper) | `$1 |", is evaluated as "some string".ToUpper, which puts the array of overload definitions for the ToUpper method on System.String in the replace string.
To keep the replace operation as a one-liner, Joey's answer using the MatchEvaluator overload to Regex.Replace works well. Or you might do the string formatting yourself based on the results of a -match:
if( '456,Jane Doe' -match '^(\d{3}),(.*)$' ) {
'| {0} | {1} |' -f $matches[2].ToUpper(),$matches[1]
}
If this needs to be replaced in the context of a larger string, you can always do a literal replace to get the final result:
PS> $r = '| {0} | {1} |' -f $matches[2].ToUpper(),$matches[1]
PS> 'A longer string with 456,Jane Doe in it.'.Replace( $matches[0], $r )
A longer string with | JANE DOE | 456 | in it.