A shell script to add `safe.directory` to a `.gitconfig`

safe-directory.sh

#!/bin/sh
# Usage: ./safe-directory.sh directory [.gitconfig] [dst]
#
# `git` will throw permission errors when a repository has been cloned with a
# user different to the runtime user. This script allows adding the cloned
# repository to the `safe.directory` configuration variable without the need
# for an installed `git` binary.
#
# This can be useful on CI runners, when the repository has been cloned as the
# `root` user but the build runs inside a container that has a user different
# to `root`. There is no guarantee that the container will have `git`
# installed, hence this script.
#
# Arguments
#   directory    The directory to add to `safe.directory`
#   .gitconfig   The `.gitconfig` to parse, defaulting to `~/.gitconfig`
#   dst          Filepath to write the resulting `git `configuration,
#                defaults to the input `.gitconfig`
#
# Examples
#   ./safe-directory.sh $CI_PROJECT_DIR

set -eu

# Parse the incoming user arguments
DIRECTORY="${1}"
SRC="${2-"~/.gitconfig"}"
DST="${3-"${SRC}"}"
# shellcheck disable=SC2088,SC2249
case "${DIRECTORY}" in
"~/"*)
	SRC="${HOME}/${DIRECTORY#"~/"}"
	;;
esac
# shellcheck disable=SC2088,SC2249
case "${SRC}" in
"~/"*)
	SRC="${HOME}/${SRC#"~/"}"
	;;
esac
# shellcheck disable=SC2088,SC2249
case "${DST}" in
"~/"*)
	DST="${HOME}/${DST#"~/"}"
	;;
esac
readonly DIRECTORY SRC DST

# Initialize/check the `.gitconfig`
if ! test -f "${SRC}"; then
	touch "${SRC}"
fi
if ! test -f "${SRC}"; then
	printf >&2 "'%s' is not a normal SRC" "${SRC}"
	exit 2
fi

# Write into a temporary file
TMP="$(mktemp /tmp/gitconfig.XXXXXXXXXX)"
readonly TMP
trap 'rm ${TMP}' EXIT

# For each line in the configuration
# Detect any previous `[safe]` section
# Insert the directory
while IFS= read -r LINE; do
	# Process the `[safe]` section
	if ! "${SAFE-true}"; then
		case "${LINE}" in
		*"directory"*)
			if test "${LINE##*= }" != "${DIRECTORY}"; then
				printf "%s\n" "${LINE}" >>"${TMP}"
				continue
			fi
			;;
		*)
			printf "Adding '%s' to '%s'\n" "${DIRECTORY}" "${SRC}"
			;;
		esac
		SAFE=true
		printf "\tdirectory = %s\n" "${DIRECTORY}" >>"${TMP}"
		continue
	fi

	# Detect the `[safe]` section
	case "${LINE}" in
	"[safe]"*)
		printf "%s\n" "${LINE}" >>"${TMP}"
		SAFE=false
		;;
	*)
		printf "%s\n" "${LINE}" >>"${TMP}"
		;;
	esac
done <"${SRC}"

# Add the `[safe]` header if, needed
if test "null" = "${SAFE-null}"; then
	printf "[safe]\n" >>"${TMP}"
	SAFE=false
fi

# If the directory was never found then add it
if ! "${SAFE:-true}"; then
	printf "Adding '%s' to '%s'\n" "${DIRECTORY}" "${SRC}"
	printf "\tdirectory = %s\n" "${DIRECTORY}" >>"${TMP}"
fi

# Copy over the temporary file
cp "${TMP}" "${DST}"