Powershell - Regex match multiple lines from file - regex

Question

I am able to match and replace multiple lines if the text string is part of the powsershell script:
$regex = #"
(?s)(--match from here--.*?
--up to here--)
"#
$text = #"
first line
--match from here--
other lines
--up to here--
last line
"#
$editedText = ($text -replace $regex, "")
$editedText | Set-Content ".\output.txt"
output.txt:
first line
last line
But if I instead read the text in from a file with Get-Content -Raw, the same regex fails to match anything.
$text = Get-Content ".\input.txt" -Raw
input.txt:
first line
--match from here--
other lines
--up to here--
last line
output.txt:
first line
--match from here--
other lines
--up to here--
last line
Why is this? What can I do to match the text read in from input.txt? Thanks in advance!

Answer 1

Using a here-string the code depends on the kind of newline characters used by the .ps1 file. It won't work if it doesn't match the newline characters used by the input file.
To remove this dependency, define a RegEx that uses \r?\n to match all kinds of newlines:
$regex = "(?s)(--match from here--.*?\r?\n--up to here--)"
$text = Get-Content "input.txt" -Raw
$editedText = $text -replace $regex, ""
$editedText | Set-Content ".\output.txt"
Alternatively you may use a switch based solution, so you can use simpler RegEx pattern:
$include = $true
& { switch -File 'input.txt' -RegEx {
'--match from here--' { $include = $false }
{ $include } { $_ } # Output line if $include equals $true
'--up to here--' { $include = $true }
}} | Set-Content 'output.txt'
The switch -File construct loops over all lines of the input file and passes each one to the match expressions.
When we find the 1st pattern we set an $include flag to $false, which causes the code to skip over all lines until after the 2nd pattern is found, which sets the $include flag back to $true.
Writing $_ on its own causes the current line to be outputted.
We pipe to Set-Content to reduce memory footprint of the script. Instead of reading all lines into a variable in memory, we use a streaming approach where each processed line is immediately passed to Set-Content. Note that we can't pipe directly from a switch block, so as workaround we wrap the switch inside a script block (& { ... } creates and calls the script block).
The idea has been adopted from this GitHub comment.