dirsums

#!/bin/bash

set -euo pipefail

usage() {
    cat >&2 <<EOM
usage: $(basename "$0") DIRECTORY...

Run checksum (sha256 by default) over all files in a directory. This is roughly
equivalent to \`find DIRECTORY -type f -print0 | xargs -0 sha256sum\`.

Do NOT pass this program untrusted DIRECTORY names, because they could be used
to instruct find(1) to run arbitrary commands.

options:
    -h       show this help message
    -a ALGO  Use ALGO for checksums
    -L       Follow symlinks -- see find(1) -L
EOM
}

get_bsd_cmd() {
    case "$1" in
        md5)    echo md5 -r ;;
        sha1)   echo shasum -a 1 ;;
        sha224) echo shasum -a 224 ;;
        sha256) echo shasum -a 256 ;;
        sha384) echo shasum -a 384 ;;
        sha512) echo shasum -a 512 ;;
        *)
            echo >&2 "Unknown algo $1"
            return 3
            ;;
    esac
}

get_gnu_cmd() {
    case "$1" in
        md5)    echo md5sum ;;
        sha1)   echo sha1sum ;;
        sha224) echo sha224sum ;;
        sha256) echo sha256sum ;;
        sha384) echo sha384sum ;;
        sha512) echo sha512sum ;;
        *)
            echo >&2 "Unknown algo $1"
            return 3
            ;;
    esac
}

algo=sha256
find_opts=()

while getopts a:hL OPT; do
    case "$OPT" in
        a)  algo="$OPTARG" ;;
        h)
            usage
            exit 0
            ;;
        L)
            find_opts+=("-L")
            ;;
        \?)
            echo >&2 "Unknown option $OPT"
            usage
            exit 1
            ;;
    esac
done

shift $((OPTIND-1))

if [ $# -eq 0 ]; then
    usage
    exit 1
fi

case "$OSTYPE" in
    darwin*)
        cmd=( $(get_bsd_cmd "$algo") )
        ;;
    *)
        cmd=( $(get_gnu_cmd "$algo") )
        ;;
esac

find_opts+=("$@")

set -x
find "${find_opts[@]}" -type f -print0 | xargs -0 "${cmd[@]}"