Question

There’s a GNU program called sponge that soaks up input before writing to a file so you can do something like this: cat myFile | grep "myFilter" | sponge myFile

Is there a powershell equivalent, so I can work on a file in place, without having to pipe to a temporary file?

Thanks

Answer 1

In Powershell, judicious use of parentheses will force an operation to completely finish before passing data to the next command in the pipeline. The default for piping Get-Content is to pipe line by line to the next command, but with parentheses it must form a complete data set (e.g., load all lines) before continuing:

(Get-Content myFile) | Select-String 'MyFilter' | Set-Content myFile

An alternative that may use less memory (I have not benchmarked it) is to only force the results of Select-String to complete before continuing:

(Get-Content myFile | Select-String 'MyFilter') | Set-Content myFile

You could also assign things to a variable as an additional step. Any technique will load the contents into the Powershell session’s memory, so be careful with big files.

Addendum: Select-String returns MatchInfo objects. Using Out-File adds pesky extra blank lines due to the way it tries to format the results as a string, but Set-Content correctly converts each object to its own string as it writes, producing better output. Being that you’re coming from *nix and are used to everything returning strings (whereas Powershell returns objects), one way to force string output is to pipe them through a foreach that converts them:

(Get-Content myFile | Select-String 'MyFilter' | foreach { $_.tostring() }) | Set-Content myFile