add-submodule

#!/bin/bash

# check whether we got the expected number of arguments
if [ "$#" == 0 ] || [ "$#" -gt 2 ]; then
  cat << EOM
  Add a git submodule from a GitHub HTTPS URL to the current repo.

  The URL is converted to use SSH instead of HTTPS.
  The submodule is checked out in its own subdirectory.
  Tabs are replaced with spaces in the relevant .gitmodules.

  Usage: $(basename "$0") GITHUB_URL [SUBMODULE_PATH]
EOM
  exit 1
fi

# check whether we're currently in a git directory
if ! GIT_DIR=$(git rev-parse --show-toplevel 2> /dev/null); then
  echo "Must be in git dir to add submodule!"
  exit 1
fi

# check whether we got a https github URL
if ! [[ $1 =~ ^https://github.com/ ]]; then
  echo "Must use a HTTPS URL from GitHub"
  exit 1
fi

URL="git@github.com:${1:19}"
REPO_NAME=${URL##*/}
if [ -z "$2" ]; then
  PATH_ARG="."
else
  PATH_ARG="${2%/}"
fi
MODULE_PATH="$PATH_ARG/$REPO_NAME"
COMMAND="git submodule add $URL $MODULE_PATH"
GIT_MODULES="$GIT_DIR/.gitmodules"

echo "Executing \`$COMMAND\`..."
eval "$COMMAND"

echo "Replacing tabs with spaces in $GIT_MODULES..."
sed -i 's/\t/  /g' "$GIT_MODULES"

echo "Adding $GIT_MODULES to index..."
git add "$GIT_MODULES"