#!/bin/bash
# validAlphaNum--Ensures that input consists only of alphabetical
#  and numeric characters

validAlphaNum()
{
    # Validate arg: returns 0 if all upper+lower+digits; 1 otherwise

    # Remove all unacceptable chars.
    validchars="$(echo $1 | sed -e 's/[^[:alnum:]]//g')"

    if [ "$validchars" = "$1" ] ; then
        return 0
    else
        return 1
    fi
}

# BEGIN MAIN SCRIPT--DELETE OR COMMENT OUT EVERYTHING BELOW THIS LINE IF
#  YOU WANT TO INCLUDE THIS IN OTHER SCRIPTS.
# =================
/bin/echo -n "Enter input: "
read input

# Input validation
if ! validAlphaNum "$input" ; then
    echo "Please enter only letters and numbers" >&2
    exit 1
else
    echo "Input is valid."
fi

exit 0