#!/bin/sh

letters()
{
    grepped=$(echo "$1" | grep -E "^[a-zA-Z]+$")
    [ "$1" = "$grepped" ] && return 0 || return 1
}

empty()
{
    if echo "$1" | grep -qE '^[[:space:]]+$'; then
        return 0
    fi
    return 1
}

digit()
{
    grepped=$(echo "$1" | grep -E "^[0-9]$")
    [ "$1" = "$grepped" ] && return 0 || return 1
}

number()
{
    grepped=$(echo "$1" | grep -E "^[1-9][0-9]+$")
    [ "$1" = "$grepped" ] && return 0 || return 1
}

alph()
{
    grepped=$(echo "$1" | grep -E "^[a-zA-Z0-9]+$")
    [ "$1" = "$grepped" ] && return 0 || return 1
}

while IFS='' read -r str; do
    if [ -z "$str" ]; then
        echo it is empty
        continue
    elif letters "$str"; then
        echo "it is a word"
    elif number "$str"; then
        echo "it is a number"
    elif digit "$str"; then
        echo "it is a digit"
    elif empty "$str"; then
        echo "it is empty"
    elif alph "$str"; then
        echo "it is an alphanum"
    else
        echo "it is too complicated"
        exit
    fi
done