makesums

#!/bin/sh

# Make sha256 checksum files

usage() {
    cat >&2 <<EOM
usage: $(dirname "$0") FILE...

Create individual checksum files for each FILE at FILE.$ALGO
EOM
}

run_sha256() {
    if which sha256sum >/dev/null; then
        run sha256sum "$@"
    elif which shasum >/dev/null; then
        run shasum -a 256 "$@"
    else
        echo >&2 "Could not find sha256sum or shasum"
        return 2
    fi
}

ALGO=sha256

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

for i in "$@"; do
    sumfile="$i.$ALGO"
    if [ -s "$sumfile" ]; then
        cat "$sumfile"
        continue
    fi

    case "$ALGO" in
        sha256)
            run_sha256 "$i" | tee "$sumfile"
            ;;
        *)
            echo >&2 "Unexpected ALGO $ALGO"
            exit 5
            ;;
    esac
done