brainfuck interpreter in posix sh

bfsh

#!/bin/sh

LANG=C

compile() {
  # some preprocessing and basic optimizations
  code=$(printf %s "$1" |
         (tr -dc '\133\135<>,.+-'; echo) | # ksh's builtin tr doesn't like []<>,.+-
         sed -e :a -e 's/<>//g;s/><//g;s/+-//g;s/-+//g
                       s/\[-]/z/g;s/zzz*/z/g;s/[+-]z/z/g;ta')

  while [ "$code" ]; do
    case $code in
      '['*) echo 'while [ "$((t$p))" != 0 ]; do :' ;; # add : for []
      ']'*) echo 'done' ;;
      '.'*) echo 'putchar' ;;
      ','*) echo 'getchar' ;;
      'z'*) echo ': "$((t$p=0))"' ;;
      '+'*) rle=1
            while case $code in '++'*) ;; *) false ;; esac; do code=${code#?} rle=$((rle+1)); done
            echo ': "$((t$p=(t$p+'"$rle"')&255))"' ;;
      '-'*) rle=1
            while case $code in '--'*) ;; *) false ;; esac; do code=${code#?} rle=$((rle+1)); done
            echo ': "$((t$p=(t$p-'"$rle"')&255))"' ;;
      '>'*) rle=1
            while case $code in '>>'*) ;; *) false ;; esac; do code=${code#?} rle=$((rle+1)); done
            echo 'p=$((p+'"$rle"'))' ;;
      '<'*) rle=1
            while case $code in '<<'*) ;; *) false ;; esac; do code=${code#?} rle=$((rle+1)); done
            echo 'p=$((p-'"$rle"'))' ;;
    esac
    code=${code#?}
  done
}

getchar() {
  # some od versions print spaces or leading zeros with -tu1
  input=$(dd bs=1 count=1 2>/dev/null | od -An -tu1 | sed 's/^ *0*//')
  : "$((t$p=input))"
}

putchar() {
  : "$((output=t$p))"
  printf "\\$(printf %03o "$output")"
}

p=0
code=$(compile "$(cat "$1")")
eval "$code"