get commit message in git hook

In the pre-commit hook, the commit message usually hasn't been created yet ¹. You probably want to use one of the prepare-commit-msg or commit-msg hooks instead. There's a nice section in Pro Git on the order in which these hooks are run, and what you typically might do with them.

_{1. The exception is that the committer might have supplied a commit message with -m, but the message still isn't accessible to the pre-commit hook, whereas it is to prepare-commit-msg or commit-msg}

The hook name should be:

commit-msg , otherwise it won't get invoked:

I have created a commit-msg script in Bash having the commit syntax <CURRENT_BRANCH_NAME>-<4_DIGIT_TICKETID>-<COMMIT_DECRIPTION>. This syntax can be used for Azure DevOps ticket ID-based commits by the developer.

#!/bin/sh

# The below input_file is file ".git/COMMIT_EDITMSG" where commits are stored
INPUT_FILE=$1

# It will copy the commit string from ".git/COMMIT_EDITMSG"
START_LINE=`head -n1 $INPUT_FILE`

# Initial index value
sum=0

# Add commit in an array variable separated by -
IFS='- ' read -r -a array_value <<< "$START_LINE"

# Count array index
for i in ${!array_value[@]}
do
    sum=`expr $sum + $i`
done

# Verify commit
if [ ${sum} == 3 ]; then

BRANCH_NAME=`git branch | awk '/\*/ { print $2; }'`
TICKET_DIGIT=`awk -F '[0-9]' '{print NF-1}' <<< "${array_value[1]}"`

   if [ ${array_value[0]} != ${BRANCH_NAME} ];  then
        echo "please enter current branch name"
        exit 1
   fi

   if [ "${TICKET_DIGIT}" != "4" ];  then
        echo "INVALID TICKET ID"
        exit 1
   else
      echo "verify ticket ID ${array_value[1]}"
   fi

else
   echo "pattern must be <CURRENT_BRANCH_NAME>-<4_DIGIT_TICKETID>-<COMMIT_DECRIPTION> without space and don't use - in commit_description"
   exit 1
fi

I implemented this in the commit-msg hook. See the documentation.

commit-msg

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

Under my_git_project/.git/hooks, I added the file commit-msg (has to be this name). I added the following Bash contents inside this file which did the validation.

#!/usr/bin/env bash
INPUT_FILE=$1
START_LINE=`head -n1 $INPUT_FILE`
PATTERN="^(MYPROJ)-[[:digit:]]+: "
if ! [[ "$START_LINE" =~ $PATTERN ]]; then
  echo "Bad commit message, see example: MYPROJ-123: commit message"
  exit 1
fi