Get commit message in Git hook

Question

I would like to check the commit message before Git commit.

I use a pre-commit hook to do that, but I couldn't find the way to get the commit message in the .git/pre-commit script. How could I get it?

Answer 1

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}

Answer 2

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

Answer 3

The hook name should be:

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

Answer 4

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

Answer 5

Usually it is done by commit-msg.
This hook gives us a file which contains the commit message.
Here is a sample to reject a commit in which we have test word:

declare -r msg=$(< $1);
if grep -i test <<< "$msg" > /dev/null 2>&1; then
    echo you are not allowd to have test commit.
    exit 1;
else
    echo looks good.
    exit 0;
fi

So exit 1 does not allow git to continue and exit 0 of the hook allows git to continue.

---

Note
Here $1 is the name of that file which is : .git/COMMIT_EDITMSG

---

Answer 6

If you want to access the commit message from hooks other than commit-msg, you can read the file .git/COMMIT_EDITMSG.

Simple Python example: (Git hooks can run Python with the #!/usr/bin/env python shebang)

#!/usr/bin/env python

from pathlib import Path

print(Path(".git/COMMIT_EDITMSG").read_text())

Just make sure to get the relative path right, based on your current working directory

Answer 7

You can do the following in a pre-receive hook (for server side) using Python, and that will display the revision information.

import sys
import subprocess
old, new, branch = sys.stdin.read().split()
proc = subprocess.Popen(["git", "rev-list", "--oneline","--first-parent" , "%s..%s" %(old, new)], stdout=subprocess.PIPE)
commitMessage=str(proc.stdout.readlines()[0])