welcome.sh

#!/bin/sh
set -e -u -f
LC_ALL=C

: $((i = name = 0))
_main() {
  let name; let i
  _malloc name 100
  i=0
  printf "What is your name?\n"
  while { _getchar _$((name + i)); [ $((_$((name + i)))) != -1 ]; } && [ $((_$((name + i)))) != $__NEWLINE__ ]; do
    : $((i += 1))
  done
  : $((_$((name + i)) = __NUL__))
  printf "Hello, "
  _put_pstr __ $name
  printf "\n"
  endlet $1 i name
}

# Character constants
readonly __NUL__=0
readonly __NEWLINE__=10
# Runtime library

__stdin_buf=
__stdin_line_ending=0 # Line ending, either -1 (EOF) or 10 ('\n')
_getchar() {
  if [ -z "$__stdin_buf" ]; then          # need to get next line when buffer empty
    if [ $__stdin_line_ending != 0 ]; then  # Line is empty, return line ending
      : $(($1 = __stdin_line_ending))
      __stdin_line_ending=0                  # Reset line ending for next getchar call
      return
    fi
    IFS=                                            # don't split input
    if read -r __stdin_buf ; then                   # read next line into $__stdin_buf
      if [ -z "$__stdin_buf" ] ; then               # an empty line implies a newline character
        : $(($1 = 10))                              # next getchar call will read next line
        return
      fi
      __stdin_line_ending=10
    else
      if [ -z "$__stdin_buf" ] ; then               # EOF reached when read fails
        : $(($1 = -1))
        return
      else
        __stdin_line_ending=-1
      fi
    fi
  fi
  __c=$(printf "%d" "'${__stdin_buf%"${__stdin_buf#?}"}"); __c=$((__c > 0 ? __c : 256 + __c))
  : $(($1 = __c))
    __stdin_buf="${__stdin_buf#?}"                  # remove the current char from $__stdin_buf
}

__ALLOC=1 # Starting heap at 1 because 0 is the null pointer.

_malloc() { # $2 = object size
  : $((_$__ALLOC = $2)) # Track object size
  : $(($1 = $__ALLOC + 1))
  : $((__ALLOC += $2 + 1))
}

_put_pstr() {
  : $(($1 = 0)); shift # Return 0
  __addr=$1; shift
  while [ $((__c = _$__addr)) != 0 ]; do
    printf \\$((__c/64))$((__c/8%8))$((__c%8))
    : $((__addr += 1))
  done
}

# Local variables
__=0
__SP=0
let() { # $1: variable name, $2: value (optional)
  : $((__SP += 1)) $((__$__SP=$1)) # Push
  : $(($1=${2-0}))                 # Init
}
endlet() { # $1: return variable
           # $2...: function local variables
  __ret=$1 # Don't overwrite return value
  : $((__tmp = $__ret))
  while [ $# -ge 2 ]; do
    : $(($2 = __$__SP)) $((__SP -= 1)); # Pop
    shift;
  done
  : $(($__ret=__tmp))   # Restore return value
}

_main __