Re: case statement with non-consecutive numbers

[pauline-galea]

> Sent: Friday, April 16, 2021 at 5:24 AM
> From: "Greg Wooledge" <greg@wooledge.org>
> To: help-bash@gnu.org
> Subject: Re: case statement with non-consecutive numbers
>
> On Thu, Apr 15, 2021 at 07:13:27PM +0200, pauline-galea@gmx.com wrote:
> > > case $input in
> > >   [2-68-9]) echo "yeah, that's good, screw 7";;
> > > esac
> >
> > I struggle with what the above means, I'm afraid.
>
> [2-6] is a glob-type pattern (or "glob" for short, as long as we're
> clear that it's being used in a context where bash doesn't expand it
> to a list of filenames).  Specifically, it's a "range expression",
> meaning it matches any single character within the range "2" to "6".
>
> Let's actually go back even farther than this.
>
> The glob [ab] matches either "a" or "b".
> The glob [abcde] matches one of "a", "b", "c", "d" or "e".
>
> Since it's pretty common to want to match one of several characters that
> are consecutive within the alphabet, we have the range expression
> shorthand:
>
> The glob [a-e] matches one of "a", "b", "c", "d" or "e" -- but ONLY IF
> the current locale is set to "POSIX" or "C", or if we're using a special
> bash option that treats range expressions as if we were in the POSIX locale.
>
> But you can also combine these.
>
> The glob [a-eqz] matches one of "a", "b", "c", "d", "e", "q" or "z".

Understood, thank you.  Did understand the 2-6 and 8-9, but not the
68 part.  Now I understand.

> > > Fear not!  You can just use more than one pattern.
> > >
> > > case $input in
> > >   [3-5]|9|1[0-3]) echo "yeah, that's good";;
> > > esac
> >
> > Means I can use "|" just as for strings.
>
> They *are* strings.  That's the entire point of this.  You are matching
> strings against strings.  The fact that the strings happen to be made up
> of digits is mostly irrelevant.
>
> The glob [3-5] matches any of "3", "4" or "5".
>
> > Doing more work on this, it looks like using commas also works
> >
> >       case $k in
> >         [1-2,4-5,7])  printf "%-21s" $s   ;;
> >         [3,6,8])      printf "%-21s\n" $s ;;
> >       esac
> >
> > Would that be correct?
>
> The glob [3,6,8] matches any of "3", ",", "6" or "8".
>
> You probably did not intend to match commas in your input.  Get rid of
> those.

You are correct.  A classic example of bad programming that however gets
the correct result I intended.  This produced quite a smile about my mistake.