Pre-commit hook for eslint, linting *only* staged changes.

pre-commit.sh

#!/usr/bin/env bash
set -uo pipefail
IFS=$'\n\t'

#
# Improvements from dahjelle/pre-commit.sh:
# - does not lint deleted files,
# - lints all staged files before exiting with an error code,
# - handles spaces and other unusual chars in file names.
#
# Based also on @jancimajek's one liner in that Gist.
#

# ESLint staged changes only
git diff --diff-filter=d --cached --name-only -z -- '*.js' '*.jsx' \
  | xargs -0 -I % sh -c 'git show ":%" | ./node_modules/.bin/eslint --stdin --stdin-filename "%";'
eslint_exit=$?

if [ ${eslint_exit} -eq 0 ]; then
  echo "✓ ESLint passed"
else
  echo "✘ ESLint failed!" 1>&2
  exit ${eslint_exit}
fi

Perhaps using xargs --max-procs (and eslint >/dev/null) could speed the script up.

I was wondering if the script can be made compatible with batch / cmd as well, but I underestimated how bad cmd is.

Also, I don't see this script taking advantage of bash features, perhaps #!/usr/bin/env sh would be a more portable shebang.

@gingerplusplus You are right with xargs, although it will only matter for a lot of files. The /dev/null part discards information that may matter though. The pipefail thing is a bash feature, so it's not portable to sh. See https://www.gnu.org/software/bash/manual/html_node/Pipelines.html.

The IFS setting is not needed.

---

I don't really get the point in having git show the file and then feed it to eslint. Is that an adaption for awful command-line conventions like the one on Windows (where sh's Cygwin/MSYS and Node's MSVCRT cmdline parsing conventions differ)?

On non-DOSish systems that have an explicit concept of argv, it is safer to just do | xargs -0 ./node_modules/.bin/eslint -- since the argument boundary is enforced automatically. The substitution neglects stuff like filenames with quotation marks in them.

eslint % would lint working directory, while git show :% | eslint --stdin lints index, which is what actually is about to be committed.

would lint working directory

Why would it? eslint has a filename-receiving CLI interface too. Git diff operates on file level.

react-boilerplate/react-boilerplate#1064 (comment)

Btw., I was trying to sidestep the issue by linting before staging instead, but thedevs-network/the-guard-bot@b379aab :)