Using the test command with STDIN

test_stdin.sh

#!/usr/bin/env bash
set +H

# Using STDIN, check LINES of FILES and use the test command to filter by EXPRESSION
# Supports all EXPRESSIONS that test does.
# fn | test_stdin -f \! -d -L -s \! -ot FILEARG
# Use '!' to negate results. -ef, -ot, -nt will be read as "LINE -nt FILEARG"

if [[ $# -eq 0 ]] ; then
	# An omitted EXPRESSION defaults to false (see manpage for test)
	exit 1
fi

validate_file(){
	local f="$1"
	shift
	local -a flags=("${@}")
	local -i passed=0 must_match=$# i=0
	for (( i = 0; i < $#; i++ )); do
		if [[ "${flags[i]}" = '!' ]] ; then
			i=$((i+1))
			must_match=$((must_match-1))
			if [[ "${flags[i]}" =~ ^-(ef|nt|ot)$ ]] ; then
				i=$((i+1))
				must_match=$((must_match-1))
				if ! test "$f" "${BASH_REMATCH[0]}" "${flags[i]}" ; then
					passed=$((passed+1))
				fi
			elif ! test "${flags[i]}" "$f" ; then
				passed=$((passed+1))
			fi
			continue
		elif [[ "${flags[i]}" =~ ^-(ef|nt|ot)$ ]] ; then
			i=$((i+1))
			must_match=$((must_match-1))
			if test "$f" "${BASH_REMATCH[0]}" "${flags[i]}" ; then
				passed=$((passed+1))
			fi
			continue
		fi
		if test "${flags[i]}" "$f" ; then
			passed=$((passed+1))
		fi
	done
	return "$((must_match-passed))"
}

declare -i e_c=0
while read -r; do
	if validate_file "$REPLY" "${@}" ; then
		printf '%s\n' "$REPLY"
	else
		e_c=1
	fi
done
exit "$e_c"