Server-side commit message validation

pre-receive

#!/bin/sh

read oldrev newrev refname

NULL_SHA1="0000000000000000000000000000000000000000"
revs=""

case $oldrev,$newrev in
    *,$NULL_SHA1) # Deleting ref
        ;;
    $NULL_SHA1,*) # Initial push
        revs=$(git rev-list --no-merges $newrev);;
    *,*) # Update
        revs=$(git rev-list --no-merges $oldrev..$newrev);;
esac

bad=0
for rev in $revs; do
    # Get first non-comment line of the commit message
    fl=$(git cat-file commit $rev | sed '1,/^$/d' | head -1)
    
    # Match the line against a regex
    if ! [[ $fl =~ ^[A-Z]+-[0-9]{4}:\ .* ]]; then
        echo "Improperly formatted commit message '$fl'"
        bad=1
    fi
done

if [ $bad -eq 1 ]; then
    echo "Example of a valid commit message: 'PROJECT-1234: Message'"
    exit 1
fi