is_steal_count.sh - return true for GrabScrab steal (via letter counting)

is_steal_count.sh

#!/bin/sh
# is_steal_count.sh - return true for GrabScrab steal (via letter counting)
# Andrew Ho (andrew@zeuscat.com)
#
# Given two words, exits with zero return status if the second word is a
# GrabScrab steal for the first (see <http://grabscrab.com>).
#
# This solution counts letters and compares the letter counts, with best
# case linear performance, by total letter count.

ME=`basename "$0"`
USAGE="usage: $ME base steal"

# Main loop, run at end
main() {
    # Check for valid inputs
    [ $# -ge 2 ] || usage 'both base and steal word inputs are required'
    base=`normalize "$1"`
    [ -n "$base" ] || die 'base word must have at least one English letter'
    steal=`normalize "$2"`
    [ -n "$steal" ] || die 'steal word must have at least one English letter'

    # Shell does not offer dictionary structure, so use eval to simulate it
    for letter in `splitletters ABCDEFGHIJKLMNOPQRSTUVWXYZ`; do
        eval "count_$letter=0"
    done

    # Increment letter count for letters in steal word
    steallen=0
    for letter in `splitletters "$steal"`; do
        eval "count_$letter=\`expr \"\$count_$letter\" + 1\`"
        steallen=`expr "$steallen" + 1`
    done

    # Decrement letter count for letters in base word, exit false if not found
    baselen=0
    for letter in `splitletters "$base"`; do
        eval "count=\"\$count_$letter\""
        [ "$count" -eq 0 ] && return 1
        eval "count_$letter=\`expr \"\$count_$letter\" - 1\`"
        baselen=`expr "$baselen" + 1`
    done

    # All letters in base found; return true as long as steal is longer
    [ "$baselen" -lt "$steallen" ]
}

# Print error message and usage to stderr, exit with non-zero return status
usage() { echo "$ME: $@" 1>&2; echo "$USAGE" 1>&2; exit 1; }

# Print error message to stderr, exit with non-zero return status
die() { echo "$ME: $@" 1>&2; exit 1; }

# Given a string, output it with only uppercase English letters
normalize() { echo "$1" | tr a-z A-Z | sed 's/[^A-Z]//g'; }

# Given a string, split it into letters
splitletters() { echo "$1" | fold -w1; }

# Run main loop
main $@