Git pre-commit hook to prevent commits which change lines with a specific substring.

pre-commit

#!/bin/sh
# Released as public domain by Michael Rabbitt (github.com/mrabbitt)
#
# Suppress commits with a specific substring in changed connect.
#
# Example (to suppress commits of lines with string DONTCOMMIT):
#
#   git config hooks.dontcommit DONTCOMMIT
#

if git rev-parse --verify HEAD >/dev/null 2>&1
then
    against=HEAD
else
    # Initial commit: diff against an empty tree object
    against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

dontcommit=$(git config hooks.dontcommit)

# Redirect output to stderr.
exec 1>&2

if [ -n "$dontcommit" ] &&
   [ $(git diff -U0 --cached $against | grep -E '^(\+|-)' | grep -c ${dontcommit}) != 0 ]
then
    cat <<EOF
You attempted to commit one or more changes containing the string
'${dontcommit}'.  You can disable this check using:

    git config --unset hooks.dontcommit

EOF

    exit 1

fi