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@cander
Created May 25, 2012 04:47
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Bourne Basic - a BASIC interpreter implemented (painfully) in pure Bourne shell
#!/bin/sh
#
#
# From: allbery@ncoast.UUCP (allbery@ncoast.UUCP)
# Subject: bournebasic
# Newsgroups: comp.sources.misc
# Date: 1987-08-18 18:54:12 PST
#
# Here's a useful BASIC interpreter written in Bourne shell.
# There's no manual but this demo shows the most salient features:
#
# 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'
# work as expected. Enjoy!
#
tfiles=/tmp/bas$$
export tfiles
trap "rm ${tfiles?Bug}*; exit" 2
> ${tfiles}
echo 'Hi there!'
while true
do
echo -n '>'
read com com2 || exit
case $com in
list)
cat ${tfiles}
;;
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*)
expr=`echo $line | sed 's/print\ *//'`
case $expr in
\"*)
echo -n `echo "$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
bc < ${tfiles}.ex > ${tfiles}.res
cat ${tfiles}.res
;;
esac
;;
if*)
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
;;
end*)
echo 0 > ${tfiles}.ln
exit
;;
goto*)
expr=`echo $line | sed 's/goto\ *//'`
echo $expr > ${tfiles}.ln
exit
;;
input*)
var=`echo $line | sed 's/input\ *//'`
echo -n "?"
echo -n "$var=" > ${tfiles}.$var
while true
do
read val
echo $val
break
done < /dev/tty >> ${tfiles}.$var
;;
*)
> ${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
echo -n $var= > ${tfiles}.$var
cat ${tfiles}.res >> ${tfiles}.$var
;;
esac
read lineno line || exit
done
done < ${tfiles}
case `cat ${tfiles}.ln` in
0*)
break
;;
*)
;;
esac
done
;;
new)
>${tfiles}
;;
quit)
echo 'Thank you for your patience.'
rm ${tfiles?Bug}*
exit
;;
load)
cp $com2 ${tfiles}
;;
save)
cp ${tfiles} $com2
;;
[0-9]*)
echo $com $com2 > ${tfiles}.nl
grep -v "^$com" ${tfiles} >> ${tfiles}.nl
sort -n ${tfiles}.nl > ${tfiles}
;;
"")
;;
*)
echo 'Illegal command'
esac
done
@cander
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cander commented May 25, 2012

I pulled this down off of Usenet back in the day - i.e., long before the Internet was open to commercial riff-raff. Because this script is so painful and slow, I was inspired to design a BASIC interpreter in NAWK (New AWK), which I never implemented. But, I did implement it in Perl - it was my first major Perl program. I'll see if I can find that, too.

@KedalionDaimon
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10 print "hello"
20 goto 10

does not seem to work, i.e. I think there is some issue with "goto".

@cander
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cander commented Jan 18, 2023

Hey @KedalionDaimon - this script is 35 years old. I put it up here to save it because I thought it was an awesome abuse of the shell.

At this point, I'd be surprised if it did work. I'll bet the problem is related to the original Bourne shell vs. modern shells like Bash.

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