Add a Git hook on Windows

Git Hooks are scripts that Git runs for you when certain actions occur.

At root of every repo, there’s a .git directory. Inside, there’s a folder called hooks that contains a bunch of files named things like pre-commit.sample. Each of those files is an example of a Git Hook. To create one for real, create a file of the same name without the extension, and Git will automatically run the script for you at the appropriate time.

At least, that’s what I thought would happen when I tried adding this pre-commit hook on Windows:

npm run typecheck

When I tried to commit it, though, I kept getting this error:

'pre-commit' is not recognized as an internal or external command,
operable program or batch file.

I tried running attrib +x .git\hooks\pre-commit, changing the extension to .bat and a bunch of other things that didn’t work before stumbling upon this StackOverflow answer that held the key: Git for Windows has an embedded bash shell!

The fix turned out to be just adding a hashbang to the top of the script and write it as though it were a Unix shell script:

#!/bin/sh
npm run typecheck