Append ticket number using git commit hooks?

You can as well use prepare-commit-msg hook, which accepts more parameters than commit-msg. Then you can check if the message is coming from a file, a template, etc to avoid appending the issue numbers when you don't want it.

With the following script in .git/hooks/prepare-commit-msg when you are working in a feature branch named foo-123, then [#123] will be added to the third line of every commit you make.

More information in this post I wrote

#!/bin/sh

if [ x = x${2} ]; then
  BRANCH_NAME=$(git symbolic-ref --short HEAD)
  STORY_NUMBER=$(echo $BRANCH_NAME | sed -n 's/.*-\([0-9]\)/\1/p')
  if [ x != x${STORY_NUMBER} ]; then
    sed -i.back "1s/^/\n\n[#$STORY_NUMBER]/" "$1"
  fi
fi

This way you can add branch name to the start of commit message. It's prepare-commit-msg hook. Work both for "git commit -m" and "git commit" commands. The option is file .git/hooks/pre-commit.skip which contains a list of branches you don't want to auto-prepend.

BRANCH="$(git rev-parse --abbrev-ref HEAD)"
FILE_CONTENT="$(cat $1)"
skip_list=`git rev-parse --git-dir`"/hooks/pre-commit.skip"
if grep -E "^$BRANCH$" $skip_list; then
  exit
fi
if [ $2 = "message" ]; then
  echo $BRANCH: $FILE_CONTENT > $1
else
  echo $BRANCH: > $1
  echo $FILE_CONTENT >> $1
fi

You missed a hook. The one you want is commit-msg:

This hook is invoked by git commit, and can be bypassed with --no-verify option. It takes a single parameter, the name of the file that holds the proposed commit log message. Exiting with non-zero status causes the git commit to abort.

So for example:

#!/bin/sh

ticket=$(git symbolic-ref HEAD | awk -F- '/^issue-/ {print $2}')
if [ -n "$ticket" ]; then
    echo "ticket #$ticket" >> $1
fi

That's a very naive parsing of your branch name, and it's simply appended to the commit message on its own line. Modify it if that's not good enough for you.

Of course, I'd actually recommend doing this in prepare-commit-msg, and committing with git commit (without -m). It's very, very rare that you can actually write sufficient information in a single-line commit message. Further, that will let you see the message before the commit is made, in case your hook doesn't do quite what you want.