Ruby style guide git pre-commit hook using Rubocop as the style guide checker. Only runs on staged ruby files that have been added and/or modified.

rubocop_pre_commit_hook

#!/usr/bin/env ruby

require 'english'
require 'rubocop'

ADDED_OR_MODIFIED = /A|AM|^M/.freeze

changed_files = `git status --porcelain`.split(/\n/).
    select { |file_name_with_status|
      file_name_with_status =~ ADDED_OR_MODIFIED
    }.
    map { |file_name_with_status|
      file_name_with_status.split(' ')[1]
    }.
    select { |file_name|
      File.extname(file_name) == '.rb'
    }.join(' ')

system("rubocop #{changed_files}") unless changed_files.empty?

exit $CHILD_STATUS.to_s[-1].to_i

You can use git diff --diff-filter AM --name-only to list the modified files.
But I would like to show only issues of changed lines, not files.

@mklink to only show changed lines, you'll need to write something up yourself, I haven't found anything out there I'm happy with.

E.g., something that:

1. Collects all the changed ruby file names in diff
2. Collects all the changed lines in the diff. E.g., for @@ -98,20 +98,20 @@ it would be lines 98..107.
3. Maps the changed lines to their file name
4. Runs rubocop on those changed file names
5. Filters the rubocop output to only show offenses that match a file/line combo from step 3

fwiw $CHILD_STATUS.exitstatus seems to work just as well, see https://ruby-doc.org/core-2.2.3/Process/Status.html

Needed to change require "english" to require "English"

I'm using this to run against staged files only: https://gist.github.com/drmartell/a45a0d277921943aab91c6b593956de4