Summary of the new feature/enhancement

Currently, a pipeline like this is impossible:

Get-Content $Path | ForEach-Object { $_ -f $a } | Set-Content $Path

This is due to Get-Content not releasing its file handle until the completion of its pipeline. Adding parentheses around the Get-Content call to force it to run to completion and collect output before proceeding does work but is a bit clunky, and there's no reason that this shouldn't also work:

Get-Content $Path -Raw | ForEach-Object { $_ -f $a } | Set-Content $Path

Currently this doesn't, because the file handle is still not released until the pipeline's completion, despite all the data being read at once. There are other caveats to using -Raw, but this would at least enable simple operations with less clunky syntax.

Proposed technical implementation details (optional)

Something that will help alleviate the issue a little bit is some of the changes to command disposal behaviour in #9900, which causes commands to be disposed as soon as their role in the pipeline is fully completed (after EndProcessing / end{} is completed).

Beyond that, the rest of the changes can be implemented in Get-Content itself for -Raw, and it may be worth looking into whether there are other avenues for alleviating the issue.

For example, in Set-Content we can have a fallback behaviour whereby if it can't get a write handle on the file, it instead writes to a temporary file, and during EndProcessing() or with a Dispose() step it then copies the file over the original.