In other words: starts with one or more alphabets/digits, followed by exactly one period, followed by 2 or more alphabets, and ends. Everything else should fail the test.
Then I also need to replace the period in the argument with an underscore.
So far I can check if the argument is empty:
case $1 in
'') echo "No argument supplied" >&2; exit 1 ;;
I figure the pattern test would need to be negated and put after the
check in that case statement, but I have no clue how to construct it. Any direct help or online resources would be greatly appreciated.
I would also like any help possible with how I can then change the valid argument supplied to replace the single period in it with an underscore.