Why isn't my git pre-commit hook trimming white space from the end of lines?

Question

I'm on Mac Mojave. I have created a file at ~/.git-templates/hooks/pre-commit , which I wanted to remove white space from the end of lines in files I'm committing. I would like this to happen globally, across all of my projects.

# A git hook script to find and fix trailing whitespace in your commits. Bypass
# it with the --no-verify option to git-commit.

# detect platform
platform="win"
uname_result=`uname`
if [[ "$uname_result" == "Linux" ]]; then
  platform="linux"
elif [[ "$uname_result" == "Darwin" ]]; then
  platform="mac"
fi

# change IFS to ignore filename's space in |for|
IFS="
"

# remove trailing whitespace in modified lines
for line in `git diff --check --cached | sed '/^[+-]/d'` ; do
  # get file name
  if [[ "$platform" == "mac" ]]; then
    file="`echo $line | sed -E 's/:[0-9]+: .*//'`"
    line_number="`echo $line | sed -E 's/.*:([0-9]+).*/\1/'`"
  else
    file="`echo $line | sed -r 's/:[0-9]+: .*//'`"
    line_number="`echo $line | sed -r 's/.*:([0-9]+).*/\1/'`"
  fi

  # since $file in working directory isn't always equal to $file in index,
  # we backup it; thereby we can add our whitespace fixes without accidently
  # adding unstaged changes
  backup_file="${file}.working_directory_backup"
  cat "$file" > "$backup_file"
  git checkout -- "$file" # discard unstaged changes in working directory

  # remove trailing whitespace in $file (modified lines only)
  if [[ "$platform" == "win" ]]; then
    # in windows, `sed -i` adds ready-only attribute to $file (I don't kown why), so we use temp file instead
    sed "${line_number}s/[[:space:]]*$//" "$file" > "${file}.bak"
    mv -f "${file}.bak" "$file"
  elif [[ "$platform" == "mac" ]]; then
    sed -i "" "${line_number}s/[[:space:]]*$//" "$file"
  else
    sed -i "${line_number}s/[[:space:]]*$//" "$file"
  fi
  git add "$file" # to index, so our whitespace changes will be committed

  # restore unstaged changes in $file from its working directory backup, fixing
  # whitespace that we fixed above
  sed "${line_number}s/[[:space:]]*$//" "$backup_file" > "$file"
  rm "$backup_file"

  [[ "$platform" == "mac" ]] || e_option="-e" # mac does not understand -e
  echo $e_option "Removed trailing whitespace in \033[31m$file\033[0m:$line_number"
done

echo

# credits:
# https://github.com/philz/snippets/blob/master/pre-commit-remove-trailing-whitespace.sh
# https://github.com/imoldman/config/blob/master/pre-commit.git.sh

# If there still are whitespace errors, print the offending file names and fail.
exec git diff-index --check --cached $against --

# Now we can commit
exit

So the problem is that it is not trimming the white space at the end of lines. When I open my file after doing a commit, I still see the white space. So my quesiton is how do I fix this? Did I put the hook at the wrong location or is there something else I need to be doing in my file?

Answer 1

Regarding your script : on your last instrcution before exiting, you probably wanted to call git diff rather than git diff-index, didn't you ?

---

Regarding the action "removing trailing whitespaces from my files before committing" :

• most editors allow to run this action on file save, and it is probably the simplest way to have your trailing spaces removed from files you edited yourself

• using git specific triggers : a more adapted way would be to use a clean filter in git attributes (see the Keyword Expansion section of the git book) :

This would apply the changes when you "git add" each file, rather than when you commit :

# choose a name for your filter (e.g : 'trimspace'), and write
# the two 'clean' and 'smudge' action :
$ git config filter.trimspace.clean 'sed -e "s/[[:space:]]*$//g"'
$ git config filter.trimspace.smudge cat

# edit the `.gitattributes` file at the root of your repo,
# and target all the files you may want to trim :
$ cat .gitattributes
*.txt filter=trimspace
*.c filter=trimspace
*.py filter=trimspace
...

# from now on : running `git add` will auto trim targeted files when
# they are added to the index

Answer 2

First, make sure the hook is in a folder referenced by a global hook path (available since Git 2.9)

git config --global core.hooksPath /path/to/my/centralized/hooks

Then, check the pre-commit hook is executable, and actually runs: Add at least one echo at the start, to validate its execution on a commit.