filter

#!/usr/bin/env nix-shell
#! nix-shell -i bash -p bash xe coreutils
# shellcheck shell=bash

export PS4='$ '

# shellcheck disable=SC2120
usage() {
    # shellcheck disable=SC2059
    [[ "$#" -eq 0 ]] || printf "$@" >&2

    cat >&2 <<EOF
usage: filter [!] <command...>
       stest [!] <test(1) arguments>

Test each item given on standard input against <command>,
and print item if <command> exits positively.

If the arguments begin with "!", their result will be
negated; this means that items will be printed if the
<command> exited unsuccessfully.

Kylie McClain <kylie@somas.is>
EOF
    [[ "$#" -eq 0 ]] || exit 1
    exit 64 # EX_USAGE
}

set -euo pipefail

sh_conjunct='&&'

# shellcheck disable=SC2119
case "$1" in
    --help) usage ;;
    '!')
        sh_conjunct='||'
        shift
        ;;
esac

pe() {
    xe -LL -j0 "$@" | sort -snk1 | cut -d' ' -f2-
}

case "${0##*/}" in
    stest)
        test_error=
        # shellcheck disable=SC2065,SC2319
        test "$@" >/dev/null 2>&1 || test_error=$?
        if [[ "${test_error}" -eq 2 ]]; then
            # syntax error; test only exits with 1 in bash on files not testing positively
            exec test "$@"
        fi

        set -- test "$@"
        ;;
esac

set -- "${@@Q}"

# shellcheck disable=SC2016,SC2145
exec pe -s "$*"' "$1" '"$sh_conjunct"' printf "%s\n" "$1"'