Re: Interaction between pre-commit hook and git commit <pathspec>

["Kristoffer Haugsbakk" <kristofferhaugsbakk@fastmail.com>]

On Tue, Nov 3, 2026, at 20:58, Kevin Lyles wrote:
> Hello, folks,
>
> The documentation for the pathspec option of the commit command claims:
> "The contents of these files are also staged for the next commit on top
> of what have been staged before."
> However, that appears to only be true if the pre-commit hook doesn't
> modify the index contents.
>
> Here's an example pre-commit script:
>     #!/bin/sh
>    
>     git diff --staged --name-only | while read -r file
>     do
>       {
>         git cat-file blob :"$file"
>         echo '# Extra text'
>       } |
>         {
>           echo -n "100644 blob "
>           echo -n $(git hash-object -w -t blob --path "$file" --stdin)
>           echo -e "\t$file"
>         } |
>           git update-index --index-info
>       echo '# Extra text' >> "$file"
>     done
>
> This always appends "# Extra text" to the end of any staged files, in
> both the index and the worktree. It serves to illustrate the issue,
> without getting into the weeds of what my pre-commit hook is doing.
> Suffice to say that my hook is (sometimes) modifying files in both the
> index (to make sure the updated contents are committed) and the
> worktree (to reduce spurious diffs when file contents are changed).
>[snip]

Reading githooks documentation for
pre-commit. To me it reads like the use case
is validation/checking, not any mutation.
This doesn't sound like a reasonable use case.