Shell: Checking if argument exists and matches expression

Question

I'm new to shell scripting and trying to write the ability to check if an argument exists and if it matches an expression. I'm not sure how to write expressions, so this is what I have so far:

#!/bin/bash

if [[ -n "$1"] && [${1#*.} -eq "tar.gz"]]; then
  echo "Passed";
else 
  echo "Missing valid argument"
fi

To run the script, I would type this command:

# script.sh YYYY-MM.tar.gz

I believe what I have is

1. if the YYYY-MM.tar.gz is not after script.sh it will echo "Missing valid argument" and
2. if the file does not end in .tar.gz it echo's the same error.

However, I want to also check if the full file name is in YYYY-MM.tar.gz format.

Answer 1

if [[ -n "$1" ]] && [[ "${1#*.}" == "tar.gz" ]]; then

-eq: (equal) for arithmetic tests

==: to compare strings

See: help test

Answer 2

You can also use:

case "$1" in
        *.tar.gz) ;; #passed
        *) echo "wrong/missing argument $1"; exit 1;;
esac
echo "ok arg: $1"