Shell Programming and Scripting

  VAR="$@"
  if [ -z "${VAR//[a-zA-Z0-9]}" ]; then
    echo "VAR has only a to z, A to Z and 0 to 9!"
  else
    echo "VAR has non-alpha-numeric!"
  fi


./Test abc
VAR has only a to z, A to Z and 0 to 9!

./Test 123abc
VAR has only a to z, A to Z and 0 to 9!

./Test 123+abc
VAR has non-alpha-numeric!

./Test !abc
VAR has non-alpha-numeric!

./Test 123!
VAR has non-alpha-numeric!

while ! [ -z "${VMC_NAME//[a-zA-Z0-9]}" ] || [ -z $VMC_NAME ]
do 
    echo ""
    echo "Error! Enter a valid value or only alphanumeric characters:"
    echo ""
    read VMC_NAME
done