PowerShell: -replace, regex and ($) dollar sign woes

Question

I am in the process of converting thousands of lines of batch code into PowerShell. I'm using regex to help with this process. The problem is part of the code is:

$`$2

When replaced it just shows $2 and doesn't expand out the variable. I've also used single quotes for the second portion of replace instead of escaping the variables, same result.

$origString = @'
IF /I "%OPERATINGSYSTEM:~0,6%"=="WIN864" SET CACHE_OS=WIN864
...many more lines of batch code
'@

$replacedString = $origString -replace "(IF /I `"%)(.+)(:.+%`"==`")(.+`")(.+)","if ( $`$2 -match `"^`$4 ) {`$5 }"

$replacedString

Abducent

Just for completeness sake whenever you post a string manipulation question, It would help everyone if you could give an example of the text before the manipulation (which you have) and what the string should look like after the manipulation. – Register

Answer 1

You could try something like this:

$origString -replace "(IF /I `"%)(.+)(:.+%`"==`")(.+`")(.+)",'if ($$$2 -match "^$4" ) {$5 }'

Note the $$$2. This evaluates to $ and content of $2.

---

Some code to show you the differences. Try it yourself:

'abc' -replace 'a(\w)', '$1'
'abc' -replace 'a(\w)', "$1"  # "$1" is expanded before replace to ''
'abc' -replace 'a(\w)', '$$$1'
'abc' -replace 'a(\w)', "$$$1" #variable $$ and $1 is expanded before regex replace
                               #$$ and $1 don't exist, so they are expanded to ''

$$ = 'xyz'
$1 = '123'
'abc' -replace 'a(\w)', "$$$1`$1" #"$$$1" is expanded to 'xyz123', but `$1 is used in regex

Wailoo

I was evaluating and trying to understand your examples and I don't understand why THIS: 'abc' -replace 'a(\w)', '$1' AND THIS: 'abc' -replace 'a(\w)', "$1" is different? – Abducent

It's because '$1' and "$1" are (after you hit Enter or run the script) first parsed by PowerShell. The '$1' and "$1" are evaluated to strings according to some rules (see e.g. computerperformance.co.uk/powershell/powershell_quotes.htm and blogs.msdn.com/b/powershell/archive/2006/07/15/… ). And after that the -replace operator is executed. It's how the interpreter works. – Wailoo

Answer 2

try like this:

 $replacedString = $origString -replace "(IF /I `"%)(.+)(:.+%`"==`")(.+`")(.+)","if ( $`$`$2 -match `"^`$4 ) {`$5 }"

Claw