The hook will check if the current branch is a story branch.

commit-msg.sh

#!/bin/sh
#
# The hook will check if the current branch is a story branch.
#
# If it is then it will check the commit message if it contains the correct prefix.
#
# Correct commit message form:
#   [STORY-ID] A commit message
#
# If the commit message does not follow the from above the hook will fix it.
#
#   case 1:
#     STORY-ID A commit message > [STORY-ID] a commit message
#
#   case 2:
#     A commit message > [STORY-ID] a commit message
#

branch=$(git symbolic-ref --short HEAD)

id="___ID___"

prefix=$(echo $branch |  sed -n 's/^\('"$id"'-[0-9]\+\).*/\1/p')

if test "$prefix" != ""; then

    prefix_exists=$(grep -i "^\[$prefix\]" $1)

    if test "$prefix_exists" = ""; then

        temp="$1.tmp"
        prefix_exists=`grep -i "^$prefix" $1`

        if test "$prefix_exists" != ""; then
            sed "s/^$prefix/\[$prefix\]/" $1 > $temp
            mv $temp $1
            echo -e "INFO: Commit message prefix corrected to [$prefix]"
        else
            sed "s/^/\[$prefix\] /" $1 > $temp
            mv $temp $1
            echo -e "INFO: Commit message prefix [$prefix] inserted."
        fi
    fi
else
    echo -e "INFO: Not a story branch. Commit message prefix won't be applied."
fi