21 June 2014

Tired of accidentally checking binding.pry calls into source? Here’s a script that will take care of checking for them on your behalf. Place this in your project’s .git/hooks directory in a file called pre-commit.

.git/hooks/pre-commit

#!/bin/sh

git diff --cached --name-only | \
    GREP_COLOR='4;5;37;41' xargs grep --color --with-filename -n pry && \
    echo 'COMMIT REJECTED' && \
    exit 1
exit 0

Note: Don’t forget to chmod pre-commit u+x to make this file executable.

Let’s step through this script line by line.

#!/bin/sh

First, we use a shebang directive to specify the interpreter that will be used to run the code in this file. Since we’re writing a shell script we specify /bin/sh.

git diff --cached --name-only | \

git diff shows us any differences between the code in working directory and our previous commit. We pass it the --cached flag to show changes to files that have already been staged. The --name-only flag will print just the names of files that have been changed, rather than the actual changed contents of those files.

GREP_COLOR='4;5;37;41' xargs grep --color --with-filename -n pry && \

GREP_COLOR is an environment variable that determines the colors grep uses to highlight matches when the --color flag is given. We use xargs to feed the individual file names that resulted from the previous line to grep pry. The --with-filename and -n flags add the file name and line number to the results, respectively. We use the logical operator && to execute the next line of code only if the current line runs successfully. (I.e. If grep doesn’t find any occurances of ‘pry’, the chain stops here.)

echo 'COMMIT REJECTED' && \
exit 1

If grep does find a ‘pry’ anywhere in our staged changes, we print an error message and exit with a status of 1 for ‘error’, which tells git to terminate the commit.

exit 0

Otherwise, we exit with a status of 0 for ‘successful’, which tells git to go ahead with the commit.

Make This Hook Global

To make this hook global, run the following command and copy the script into ~/.git_template/hooks. Thereafter, every time you call git init, it will be included in your project’s .git/hooks directory.

$ git config --global init.templatedir '~/.git_template'

$ cp /myproject/.git/hooks/pre-commit ~/.git_template/hooks/pre-commit

And there you have it.