git-ignore

#!/bin/bash

# SPDX-License-Identifier: GPL-3.0-only
# Copyright 2022, Mattias Bengtsson <mattias.jc.bengtsson@gmail.com>

set -e
set -o pipefail

function usage {
    cat <<EOM
usage: git ignore [<path|pattern>...]

where:
  <path> is a regular file path.
  <pattern> is a literal gitignore pattern starting with a '/'.
EOM
}

if [[ " ${*} " == *" --help "* ]] || [[ " ${*} " == *" -h "* ]]; then
    usage
    exit
fi

# Check that we're inside a git worktree
git rev-parse --is-inside-work-tree >/dev/null
TOPLEVEL="$(git rev-parse --show-toplevel 2>/dev/null)"

if [ "${#}" -le 0 ]; then
    usage >&2
    exit 2
fi

for f in "${@}"; do
    if [ "${f:0:1}" = '/' ]; then
        # Take paths beginning with '/' as literal `.gitignore` lines
        echo "${f}"
    else
        # Resolve the rest relative to the git top directory.
        echo "/$(realpath --strip --relative-to="${TOPLEVEL}" "${f}")"
    fi
done >> "${TOPLEVEL}/.gitignore"