002-validalnum.sh

#!/bin/sh
# validalAlphaNum - Ensures that input only consists of alphabetical
#              and numeric characters.

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

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

  if [ "$compressed" != "$input" ] ; then
    return 1
  else
    return 0
  fi
}

# Sample usage of this function in a script

echo -n "Enter input: "
read input

if ! validAlphaNum "$input" ; then
  echo "Your input must consist of only letters and numbers." >&2
  exit 1
else
  echo "Input is valid."
fi

exit 0