Man Grep : conveniently search for a command's options descriptions

mg.sh

#!/bin/bash


declare -r Base_name=$(basename -s .sh "$0")


help()
{
	cat <<-EOD
Man Grep
Conveniently lookup a keyword in a man page.

Usage:
    ${Base_name} [GREP-OPTIONS... [--]] COMMAND KEYWORD

GREP-OPTIONS (optional)
    Options that will be passed directly to grep.
    You may end this list with '--' to avoid ambiguity.

COMMAND
    The name of the command of which the man page will be scanned.

KEYWORD
     The sequence of characters to search for in the man page of COMMAND.
     This could be a Grep's pattern, but will typically be just a flag.

Examples:
    ${Base_name} ls -A
    ${Base_name} -w ls -a
    ${Base_name} --color=auto -- man --warnings

	EOD
}


#
# Utilities
#
init_enum_array()
{
    declare -n Arr=$1
    shift
    declare -i i=0
    for Elem in $@;
    do
        Arr+=([$Elem]=$((i++)))
    done
}


command_exists()
{
	\type "$1" &> /dev/null
	\return $?
}


is_opt()
{
	[[ $1 =~ ^-.*$ ]]
	\return $?
}


is_opt_help()
{
	case "$1" in '--help'|'-help'|'-h'|'-?')
		\return $(true)
	esac
	\return $(false)
}


validate_color_option()
{
	Tail=${1:${#1}-4:4}

	case $Tail in 'auto'|'ever'|'ways')
		return $(true)
	esac
	\return $(false)
}


say_more_info()
{
	\echo "Type '${Base_name} --help' for usage information."
}


#
# Entry point
#
main()
{
	#
	# Command line validation, rough first pass
	#
	if is_opt_help "$1"; then
		help;
		exit 0

	elif [[ $# -lt 2 ]];
	then
		\echo "Need at least two parameters."
		say_more_info
		exit 1
	fi

	#
	# Variables for arguments parsing
	#
	declare -a Grep_flags=()
	\declare Search_flag=""
	\declare Command=""
	\declare Color_flag='--color=auto'
	\declare -i Parsing_phase
	\declare -A Phase
	init_enum_array Phase 'START GREP_OPT COMMAND KEYWORD DONE'

	#
	# Nested functions for argument parsing
	#
	parse_grep_option()
	{
		if [[ $1 = '--' ]]; then
			Parsing_phase=${Phase[COMMAND]}

		elif [[ $1 =~ ^--colou?r=.*$ ]];
		then
			if validate_color_option "$1"; then
				Color_flag="$1"
			else
				\echo "${Base_name} error: invalid color option for grep ("$1")."
				say_more_info
				\exit 2
			fi
		else
			Grep_flags+=("$1")
		fi
	}

	parse_command_name()
	{
		if is_opt "$1"
		then
			\echo "${Base_name}: error in command name ("$1"). Abort"
			say_more_info
			\exit 3
		fi
		Command="$1"
	}

	#
	# Do argument parsing
	#
	for Arg in $@;
	do
		if [[ $Parsing_phase -eq ${Phase[START]} ]];
		then
			if is_opt_help "$Arg"
			then
				help;
				exit 0

			elif [[ $Arg = '--' ]]; then
				Parsing_phase=${Phase[COMMAND]}

			elif is_opt "$Arg"; then
				Parsing_phase=${Phase[GREP_OPT]}
				parse_grep_option "$Arg"

			else
				parse_command_name "$Arg"
				Parsing_phase=${Phase[KEYWORD]}
			fi

		elif [[ $Parsing_phase -eq ${Phase[GREP_OPT]} ]];
		then
			parse_grep_option "$Arg"

		elif [[ $Parsing_phase -eq ${Phase[COMMAND]} ]];
		then
			parse_command_name "$Arg"
			Parsing_phase=${Phase[KEYWORD]}

		elif [[ $Parsing_phase -eq ${Phase[KEYWORD]} ]];
		then
			Search_flag="$Arg"
			Parsing_phase=${Phase[DONE]}

		elif [[ $Parsing_phase -eq ${Phase[DONE]} ]];
		then
			\echo "Too much search keywords."
			say_more_info
			exit 4
		fi

	done

	#
	# Check and validate parsing
	#
	if [[ $Parsing_phase -eq ${Phase[GREP_OPT]} ]];
		# Here we try to repair the situation where the user forgot to pass '--'
		# after grep options to change parsing phase.
		# So we check if flag[last-2] is not starting with '-', and try to use
		# last two flags as command name and search pattern.
	then
		GF_count=${#Grep_flags[@]}

		if [[ $GF_count -gt 1 ]] && ! is_opt "${Grep_flags[$((GF_count-2))]}"
		then
			Search_flag="${Grep_flags[$((GF_count-1))]}"
			Command="${Grep_flags[$((GF_count-2))]}"
			unset Grep_flags[-2]
			unset Grep_flags[-1]

		else
			\echo "${Base_name} error: grep flags string not terminated"\
				"(missing '--')."
			say_more_info
			exit 5
		fi

	elif [[ $Parsing_phase -eq ${Phase[COMMAND]} ]]; then
		\echo "${Base_name} error: missing command name."
		say_more_info
		exit 6

	elif [[ ${#Search_flag} -eq 0 ]]; then
		\echo "${Base_name} error: missing flag to search for."
		say_more_info
		exit 7

	fi

	#
	# Check command validity
	#
	if ! command_exists "$Command"
	then
		\echo "${Base_name} error: couldn't find or execute \"$Command\"."
		exit 8
	fi

	#
	# Configure grep
	#
	declare Grep='/usr/bin/grep'

	if [[ ! -x $Grep ]];
	then
		Grep='/bin/grep'

		if [[ ! -x $Grep ]]; then
			\echo "${Base_name} error: couldn't find grep. Abort."
			exit 9
		fi
	fi

	#
	# Exec search in command's help
	#
	$Grep "${Grep_flags[@]}" "$Color_flag" -- "${Search_flag}" <(man ${Command})

}

#
# Launch
#
main $@