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How To Prevent Unwanted Code From Ending Up In Your Commits

14th December 2016

Badger debug line

Checking the diff of the code that you're about to commit is a good habit to get into, and it's something I try do before committing any changes to the project I'm working on.

Inevitably, however, debug code does slip through the cracks. I can't tell you the number of times I've committed and pushed code, only to then spot a rogue IT WORKS! or myVar: 7 popping up in the console. It then takes a second commit to remove the code with some message along the lines of Removed debug code.

This was starting to bother me, so I decided to take action and write a simple pre-commit hook to catch any code that shouldn't be committed.


for FILE in `git diff-index --cached --name-status HEAD -- | cut -c3-` ; do
    # Check if the file contains 'XXX'
    if grep -q 'XXX' $FILE; then
        echo 'Commit failed:' $FILE 'contains XXX'
        exit 1

This code should be added to the .git/hooks directory of your git project and named pre-commit.

The code above will be triggered every time you try to commit. Before the commit is initiated, it will look through a diff of your changes for the string XXX and, if it finds it, will cause the commit to fail with an appropriate error.

Once that's set up, all you need to do is mark any of your debug lines with a comment of XXX as you write them.

// app.js
const someVar = myFunction();

// XXX
console.debug('someVar: ', someVar);

If you tried to commit this code, it would fail with the error Commit failed: app.js contains XXX.

And there you have it! You can now rest assured that none of your debug code will end up immortalised forever in your project's commit history.