Regex replace multilines in powershell

Based on feedback from Poutrathor (the OP), there were two problems:

• The primary problem was that Get-Content($filePath) (which should be written as
  Get-Content $filePath^[1]) reads the file line by line, which results in an array of lines when captured in a variable.
  -replace then operates on each input line individually, which means that the line-spanning regex won't match anything.

  • Solution: Use Get-Content -Raw (PSv3+) to read the file as a whole into a single, multi-line string.

• Secondarily, you mention needing to replace the regex newline (end-of-line) escape sequence (\n) (LF) with its PowerShell string-interpolation counterpart (`n) - note that PowerShell uses `, the backtick, as the escape character:

  • Note that that is only necessary in the replacement string, in order to create actual, literal newlines (line breaks) on output - as opposed to using regex construct \n for matching newlines.

  • However, on Windows, newlines are typically CRLF sequences, i.e., a CR (\r, `r) immediately followed by a LF (\n / `n) - i.e., \r\n/ `r`n - whereas on Unix-like platforms they are just LF, \n / `n.

    • If you're not sure which style of newlines given input has, use \r?\n to match newlines in a cross-platform-compatible manner.
      If you don't care what specific newlines the input has, this is safe to use methodically, as a matter of habit.

  • Therefore:

    • In your regex, while in your case you can choose between \r\n and `r`n, note that:

      • `r`n only works in double-quoted "..." strings.
      • It is generally preferable to use literal, single-quoted strings to store regexes - which requires use of \r\n (Windows) / \n (Unix) / \r?\n (platform-agnostic) - so that there's no confusion over which parts of the string PowerShell interpolates up front vs. which parts are interpreted by the regex engine.

    • In your replacement string, use `r`n inside "..." to create actual newlines.

As an alternative to using escape sequences to represent newlines, you can use here-strings to conveniently define multi-line strings with actual newlines (line breaks), as shown in Paweł Dyl's answer, but there's a caveat:

• Here-strings invariably have the same style of newline as the enclosing script file, which means that:
  • A regex based on a here-string will only match if the input happens to have the same style of newlines as the script file.
  • A replacement string based on a here-string will invariably use the script file's newline style.

^{[1] Your call looks like a .NET method call and while it happens to work in this case, such syntax confusion should be avoided: PowerShell cmdlets and functions are invoked like shell commands: without parentheses ((...)) and with whitespace-separated arguments.}