How to replace lines depending on the remaining text in file using PowerShell

Question

I need to edit txt file using PowerShell. The problem is that I need to apply changes for the string only if the remaining part of the string matches some pattern. For example, I need to change 'specific_text' to 'other_text' only if the line ends with 'pattern':

'specific_text and pattern' -> changes to 'other_text and pattern'

But if the line doesn't end with pattern, I don't need to change it:

'specific_text and something else' -> no changes

I know about Replace function in PowerShell, but as far as I know it makes simple change for all matches of the regex. There is also Select-String function, but I couldn't combine them properly. My idea was to make it this way:

((get-content myfile.txt | select-string -pattern "pattern") -Replace "specific_text", "other_text") | Out-File myfile.txt

But this call rewrites the whole file and leaves only changed lines.

Thank you, @WiktorStribiżew! If you want, you can write it as an answer and I'll accept it — Bashnia007
– Bashnia007, Commented Jul 27, 2020 at 9:14

Wiktor Stribiżew · Accepted Answer · 2020-07-27 10:45:04Z

1

You may use

(get-content myfile.txt) -replace 'specific_text(?=.*pattern$)', "other_text" | Out-File myfile.txt

The specific_text(?=.*pattern$) pattern matches

specific_text - some specific_text...
(?=.*pattern$) - not immediately followed with any 0 or more chars other than a newline as many as possible and then pattern at the end of the string ($).

answered Jul 27, 2020 at 10:45

Wiktor Stribiżew

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