Git hook to prevent committing xdebug_break() functions. Save as .git/hooks/pre-commit then chmod +x it. Submodules also have their own hooks folder: ".git/modules/submodule/path/here/hooks".

pre-commit

#!/bin/sh

if git-rev-parse --verify HEAD >/dev/null 2>&1; then
    against=HEAD
else
    against=4b825dc642cb6eb9a060e54bf8d69288fbee4904
fi

for FILE in `git diff --cached --name-only` ; do
    # Check if the file contains 'debugger'
    grep -qE '^[ \t]*xdebug_break()' $FILE
    if [[ $? -eq 0 ]]
    then
        echo $FILE ' contains xdebug_break()! To commit retry with --no-verify'
        exit 1
    fi
done
exit

This is perfect. Exactly what I was looking for. Thanks! (Note that it doesn't seem that the initial conditional serves any purpose, so I have removed that on my fork.)