Whose `git` is it anyway?

Question

A Posix function for finding the nearest parent file. For example "what .git/ am I working in?" or "is there an .npmrc affecting npm from this path?" This implementation specifically follows the symbolic links toward root rather than the canonical path.

Looking for improvements and potential edge cases.

lsup() {
  path="$1";
  file="$2";
  if [ -z "${file}" ]; then
    file="${path}";
    path="$(pwd)";
  fi;
  path="$(realpath -es "${path}")"
  [ -n "${SH_DEBUG}" ] && echo "Searching for ${file} from ${path}…";
  while [ "${path}" != "/" ]; do
    [ -e "${path}/${file}" ] && break;
    [ -n "${SH_DEBUG}" ] && echo "Not found in ${path}";
    path="$(realpath -s "${path}/..")";
  done;
  [ -e "${path}/${file}" ] && echo "${path}/${file}" || return 1;
}

https://gist.github.com/psaxton/6937fec3357f8295828d2e3577f9bcb6

Used as:

> lsup .git

> lsup /path/to/check .npmrc

Answer 1

First, dump all those empty statements (; followed immediately by newline).

It might be better to swap the order of arguments, so the optional one is last:

file=$1
path=$(realpath -es "${2:-$PWD}") || return 1

(No need for quotes for RHS of assignment; explicit fail instead of depending on set -e).

The conditional printing gives an error return when $SH_DEBUG is unset; turn it around so that the pipeline is always true. Expand as ${SH_DEBUG-} so that this works when set -u -e. Log output should go to standard error stream, not output.

Since we have an absolute path and we're not expanding symlinks, we can use a simple pattern substitution in the iteration, rather than :

path=${path%/*}

We could turn the loop around, so that it terminates when the file is found, instead of repeating the test.

---

Modified code

#!/bin/sh

set -eu  # will work with any combination of these flags

lsup() {
    file=${1:-}
    [ "$file" ] || return 1
    path=$(realpath -es "${2:-$PWD}") || return 1

    [ -z "${SH_DEBUG-}" ] || echo >&2 "Searching for ${file} from ${path}…"

    until [ -e "${path}/${file}" ]
    do
        [ -z "${SH_DEBUG-}" ] || echo >&2 "Not found in ${path}/"
        [ -n "$path" ] || return 1
        path=${path%/*}
    done
    echo "${path}/${file}"
}