How can I determine whether a bash variable is an option beginning with `-`.

I have two possibilities for an option, either

or

With comma (,) being the delimiter, in general -S NUM{DELIM}NUM.

Currently I have the following bash code. The function affirm-numeric determined whether the last argument is a whole number.

The problem can be solved if I can determine that "$2" contains a delimiter between the two numbers.

Maybe you should research getopts

I want to match with a pattern.

What is wrong with what was provided here:
https://www.linuxquestions.org/quest...on-4175711848/

1 members found this post helpful.

I cannot see that it provides details on how to detect variables starting with -.

By checking the contents of $3, I want to distinguish between an option defined by

and one defined by

I'm having a hard day. I missed the part about the variable.

Let met think a bit...

I don't under stand your example. What is -S?
Is num a negative number?

Have updated the question with explanation.

As rtmistler has suggested, the path to understanding shell argument processing lies in understanding the bash built-in command getopts (man getopts or man bash), and/or GNU getopt (man getopt, getopt is my personal preference).

For the case:

... you may require -S to take an argument, the first NUM, in which case the second NUM is a non-option argument. Or -S may take no arguments and both NUM's are non-option arguments. Either way you must process option arguments and non-option arguments.

In the case:

... you face the same choices for -S regardless of the presence or absence of a third argument - they are not related. You must also define -O which takes an argument (i.e. 'PT'), or PT becomes an error, the options -P and -T, or another non-option argument, depending on how you handle them!

Most of the problems are solved and handling greatly simplified by using getopts or getopt - learn how they work!

UPDATE: For the case you have added to the original post:

... NUM,NUM is a single argument value, whether or not it is an argument to -S or a non-option argument, so your code will have to detect and handle that in any case. This also implies additional cases in view of your earlier examples:

... which only complicates things! All of this is why getopts and getopt were written... so learn to use them and solve this and all future similar problems!

Basically what both do is to allow you to enforce a specification for all valid options and arguments, imposes an ordering on those options and arguments and delivers them to your processing loop in a canonical form as well as optionally trapping out input errors and invalid arguments.

getopt is a utility that can handle long options but is buggy which is why you will find DIY implementations like I posted in the other thread.
https://man7.org/linux/man-pages/man1/getopt.1.html

getopts is a builtin bash function which is much easier to use but does not handle long options.

As posted n,m is one argument and as suggested you can split the string and then do error checking to see if they are numbers.

For this scenario the easiest would to use quotes which would treat the two numbers as one argument. You would still split the string and perform the same checks as above.

2 members found this post helpful.

The following tests for a comma:
Then split and test for numeric.
If you want to avoid a further nested if clause then
just split and test, using the fact that there can be multiple statements between elif and then (the last exit status matters):

For examplethis is quite unusual. That is not a problem, just it means there is no general solution to handle it, you need to implement it yourself.
That is quite simple, you need to split $2:
But you can also do some other checks, like this:
and here you can find additional tips: https://linuxize.com/post/how-to-che...tring-in-bash/

1 members found this post helpful.