a simple git subcommand for adding files to the .gitignore

git-ignore

#!/bin/bash
#
# This file is used to ignore files and folders in git.
#
# usage:
#   git ignore
#   git ignore <file1|pattern1> <file2|pattern2> ...
#
# - If no arguments are given, the .gitignore file will be opened in your
#   default $EDITOR.
# - If an argument is an existing file, it will be added to the .gitignore file
#   using its path relative to the repository root.
# - If an argument is a pattern, it will be added to the .gitignore file as is.

GITROOT="$(git rev-parse --show-toplevel)" || exit 1
GITIGNORE="$GITROOT/".gitignore
LINES="$(wc -l "$GITIGNORE" | cut -d' ' -f1)"
LINE=$(($LINES + 1))

collapse-relative-path() {
  # remove any `dir/../` sections from the path
  path="$1"
  while [[ "$path" = *"../"* ]]; do
    path="$(echo "$path" | sed 's_/[^/]*/\.\.__')"
  done
  echo "$path"
}

# if no args provided, then just show the .gitignore file
if [ -z "$1" ]
then
  "$EDITOR" "$GITIGNORE"
else
  # loop through args and add them to .gitignore
  for path in "$@"; do
    if [ -f "$GITIGNORE" ] && [ "$(tail -c 1 $GITIGNORE; echo x)" != $'\nx' ]
    then
      # if the file doesn't end with a newline, add a newline before our entry
      echo >> "$GITIGNORE"
    fi
    if [ -e "$path" ]
    then
      # if the file is a directory, make sure it ends with a slash
      if [ -d "$path" ] && [ "${path: -1}" != "/" ]
      then
        path="$path/"
      fi
      # if the file exists, determine its path relative to the git root
      fullpath=$([[ $path = /* ]] && echo "$path" || echo "$PWD/${path#./}")
      if [[ "$fullpath" =~ "$GITROOT" ]]
      then
        path="${fullpath/$GITROOT\//}"
      fi
      # collapse any relative paths
      path="$(collapse-relative-path "$path")"
    fi
    # make sure the path doesn't already exist in the .gitignore
    line_no=$(grep -Fxn "$path" "$GITIGNORE" | cut -d: -f1 | head -n1)
    if [ -n "$line_no" ]
    then
      # if it does, then just echo a warning
      echo ".gitignore:$line_no  $path (already exists)"
    else
      # otherwise, add the path to the .gitignore
      echo "$path" >> "$GITIGNORE"
      echo ".gitignore:$LINE  $path"
      let LINE++
    fi
  done
fi