BAShIC.sh

#!/usr/bin/env bash
# BAShIC - BASIC interpreter written in Bash
# Based on bournebasic by Brandon S. Allbery 1987
# 
# 10 print "Enter any number and I will double it for you ";
# 20 input x
# 30 y = 2*x
# 40 print "The answer is ";
# 50 print y
# 60 print "Enter -1 if you want to continue."
# 70 input c
# 80 if c = -1 then 10
# 90 print "Bye"
# 
# Also, the commands 'load', 'save', 'list', 'run', and 'new'

print() {
	expr=`echo $line | sed 's/print\ *//'`
	case $expr in
		\"*)
			printf `echo "$expr" | sed 's/^\"//
									   s/\".*$//'`
			case $line in
				*\;) ;;
				*) echo ;;
			esac
			;;
		*) > ${tfiles}.ex
			files=`echo ${tfiles}.?`
			case $files in
				${tfiles}.\?)
					;;
				*)
					for i in $files; do
						cat $i >> ${tfiles}.ex;
					done
					;;
			esac
			echo $expr >> ${tfiles}.ex
			c < ${tfiles}.ex > ${tfiles}.res
			cat ${tfiles}.res
			;;
	esac
}
goto() {
	expr=`echo $line | sed 's/goto\ *//'`
	echo $expr > ${tfiles}.ln
	exit
}
input() {
	var=`echo $line | sed 's/input\ *//'`
	printf "?"
	printf "$var=" > ${tfiles}.$var
	while true; do
		read val
		echo $val
		break
	done < /dev/tty >> ${tfiles}.$var
}
if_cmd() {
	expr=`echo $line | sed '{
							s/if\ */\(/
							s/[#=]/\)-\(/
							s/\ *then.*/\)/
							}'`
	target=`echo $line | sed 's/.*then\ *//'`
	> ${tfiles}.ex
	files=`echo ${tfiles}.?`
	case $files in
		${tfiles}.\?) ;;
		*)
			for i in $files; do
				cat $i >> ${tfiles}.ex
			done
			;;
	esac
	echo $expr >>${tfiles}.ex
	res=`bc < ${tfiles}.ex`
	case $res in
		0*)
			case $line in
				*=*) echo $target > ${tfiles}.ln; exit ;;
				*) ;;
			esac
			;;
		*)
			case $line in
				*#*)
					echo $target > ${tfiles}.ln
					exit ;;
				*) ;;
			esac
			;;
	esac
}
star() {
	> ${tfiles}.ex
	files=`echo ${tfiles}.?`
	case $files in
		${tfiles}.\?) ;;
		*)
			for i in $files; do
				cat $i >> ${tfiles}.ex
			done
			;;
	esac
	echo $line >>${tfiles}.ex
	var=`echo $line | sed 's/\ *=.*//'`
	echo $var >> ${tfiles}.ex
	bc < ${tfiles}.ex > ${tfiles}.res
	printf $var= > ${tfiles}.$var
	cat ${tfiles}.res >> ${tfiles}.$var
}
run() {
	echo 0 > ${tfiles}.ln
	while true; do
		while true; do
			case `cat ${tfiles}.ln` in
				0)	read lineno line || exit ;;
				*)	while true; do
						read lineno line || exit
						match=`cat ${tfiles}.ln`
						case $lineno in
							$match)
								break ;;
							*)
								;;
						esac
					done
			esac
			while true; do
				case $line in
					print*) print ;;
					if*)    ;;
					end*)   echo 0 > ${tfiles}.ln; exit ;;
					goto*)  goto ;;
					input*) input ;;
					*)      star ;;
				esac
				read lineno line || exit
			done
		done < ${tfiles}
		case `cat ${tfiles}.ln` in
			0*) break ;;
			*)  ;;
		esac
	done
}
quit() {
	echo 'Goodbye'
	rm ${tfiles?Bug}*
	exit
}
lnumb() {
	echo $com $com2 > ${tfiles}.nl
	grep -v "^$com" ${tfiles} >> ${tfiles}.nl
	sort -n ${tfiles}.nl > ${tfiles}
}

tfiles=/tmp/bas$$
export tfiles
trap "rm ${tfiles?Bug}*; exit" 2
> ${tfiles}
echo 'BASIC'
while true; do
	printf '>'
	read com com2 || exit
	case $com in
		list)   cat ${tfiles} ;;
		run)    run ;;
		new)    >${tfiles} ;;
		quit)   quit ;;
		load)   cp $com2 ${tfiles} ;;
		save)   cp ${tfiles} $com2 ;;
		[0-9]*) lnumb ;;
		"")     ;;
		*)      echo 'Illegal command'
	esac
done