Consume a null separated list on stdin and do something with each element.

nulliter.sh

#!/bin/bash

set -e

SCRIPT_NAME="${0##./}"

# shellcheck disable=SC2120
print_help() {  
	local exit_error
	exit_error="${1:-1}"
	cat - <<EOF
For each null terminated input to stdin do something.

Usage:
	$SCRIPT_NAME -h|--help
	$SCRIPT_NAME [-d|--debug] [--allow-errors] -s|--source <bash script path>
	$SCRIPT_NAME [-d|--debug] [--allow-errors] -r|--run <executable> [-p|--argpos <arg position index>] -- [<executable args>]

Options:
	-h|--help: Show this message.
	--allow-errors: Adds 'set +e' for sourced script.
	-d|--debug: Adds 'set -x' to sourced scripts.
	-s|--source <bash script path>: Source the given bash script for each item passed to stdin. The variable \$nulliter_item containing the current line is available to the sourced script.
	-r|--run <executable>: Run an executable with the item from stdin at the position given to -p|--argpos.
	-p|--argpos <arg position index>: The position of the item in the arguments passed to the executable. Defaults to the last argument.
	--sleep: Sleep for some interval after each iteration. The value of this argument is passed to the sleep command.
	<executable args>: Arguments to pass to the executable specified with -r|--run.
EOF
	if [[ "$exit_error" != "noexit" ]]; then
		exit "$exit_error"
	fi
}

iternull_cmd() {
	local argpos executable args args_after args_before sleep_for
	args=()
	args_after=()
	args_before=()
	sleep_for="$1"
	shift
	argpos="$1"
	executable="$2"
	shift 2
	args=("$@")
	if [[ "$argpos" -eq "-1" ]]; then
		args_before=("${args[@]}")
	else
		if [[ "$argpos" =~ -[0-9]+ ]]; then
			argpos="$(( ${#args[@]} + argpos ))"
		fi
		args_before=("${args[@]::$(( argpos - 1 ))}")
		args_after=("${args[@]:$(( argpos - 1 ))}")
	fi
	if [[ "${sleep_for#}" -gt 1 ]] || [[ "$sleep_for" -gt 0 ]]; then
		sleep_cmd="sleep $sleep_for"
	else
		sleep_cmd=":"
	fi
	while IFS= read -r -d '' nulliter_line; do
		"$executable" "${args_before[@]}" "${nulliter_line}" "${args_after[@]}" || exit $?
		$sleep_cmd
	done
}

iternull_source() {
	local script bashopts set_bashopts sleep_for
	sleep_for="$1"
	shift
	script="$(realpath "$1")"
	shift 
	bashopts="$*"
	if [[ -n "$bashopts" ]]; then
		set_bashopts="set $bashopts"
	else
		set_bashopts=":"
	fi
	if [[ "${sleep_for#}" -gt 1 ]] || [[ "$sleep_for" -gt 0 ]]; then
		sleep_cmd="sleep $sleep_for"
	else
		sleep_cmd=":"
	fi
	export nulliter_item
	while IFS= read -r -d '' nulliter_item; do
		# shellcheck disable=SC1090
		(${set_bashopts}; source "$script")
		$sleep_cmd
	done
}

main() {
	local OPTS bashopts bashopts source_script run_script run_args argpos sleep_for
	run_args=()
	argpos=-1
	sleep_for=-1

	OPTS=$(getopt --name "$SCRIPT_NAME" --options hds:r:p: --longoptions help,debug,allow-errors,soruce:,run:,argpos:,sleep: -- "$@") || print_help
	eval set -- "$OPTS"
	
	while [[ "$#" -gt 0 ]]; do
		case "$1" in
			-h|--help)
				print_help
				;;
			--allow-errors)
				if [[ -n "$run_script" ]]; then
					echo 'WARNING: ignoring '"$1"'. --allow-errors is only used with -s|--source.'>&2
				else
					bashopts="${bashopts} +e"
				fi
				shift
				;;
			-d|--debug)
				if [[ -n "$run_script" ]]; then
					echo 'WARNING: ignoring '"$1"'. -d|--debug is only used with -s|--source.'>&2
				else
					bashopts="${bashopts} -x"
				fi
				shift
				;;
			-s|--source)
				if [[ -n "$run_script" ]]; then
					echo 'ERROR: -r|--run and -s|--source are mutually exclusive.'>&2
					print_help
				fi
				source_script="$2"
				shift 2
				;;
			-r|--run)
				if [[ -n "$source_script" ]]; then
					echo 'ERROR: -r|--run and -s|--source are mutually exclusive.'>&2
					print_help
				fi
				run_script="$2"
				shift 2
				;;
			-p|--argpos)
				if [[ -n "$source_script" ]]; then
					echo 'WARNING: ignoring '"$1 $2"'. -p|--argpos is only used with -r|--run.'>&2
				else
					argpos="$2"
				fi
				shift 2
				;;
			--sleep)
				sleep_for="$2"
				shift 2
				;;
			--)
				shift
				run_args=("$@")
				break
				;;
			*)
				print_help
				;;
		esac
	done
	if [[ -n "$run_script" ]]; then
		iternull_cmd "$sleep_for" "$argpos" "$run_script" "${run_args[@]}"
	elif [[ -n "$source_script" ]]; then
		iternull_source "$sleep_for" "$source_script" "$bashopts"
	fi
}

main "$@"