support/hooks/commit-msg

#!/usr/bin/env bash
#
# A hook script to verify commit message format. Called by "git commit"
# with one argument, the name of the file that has the commit message.
# The hook exits with non-zero status after issuing an appropriate
# message if it wants to stop the commit. The hook is allowed to edit the
# commit message file.
#
# To enable this hook, run `bootstrap` or do this from the root of the repo:
#
# $ ln -s ../../support/hooks/commit-msg .git/hooks/commit-msg

FIRST_LINE=$(head -n 1 $1)
LAST_CHAR=$(echo -n $FIRST_LINE | tail -c 1)
FIRST_CHAR=$(echo -n $FIRST_LINE | head -c 1)

if [[ ! "$FIRST_CHAR" =~ [A-Z] ]]; then
    echo >&2 "Error: Commit message summary (the first line) must start with a capital letter."
    exit 1
fi

LENGTH=$(echo $FIRST_LINE | wc -c)
if [ "$LENGTH" -gt "73" ]; then
    echo >&2 "Error: Commit message summary (the first line) must not exceed 72 characters."
    exit 1
fi

if [ "$LAST_CHAR" != "." ]; then
    echo >&2 "Error: Commit message summary (the first line) must end in a period."
    exit 1
fi