glob plainly emulates shell globbing, and does not work with regexen. You can either use File::Find (or its relatives File::Find::Rule and File::Finder) even if you do not need to recurse, or just opendir, readdir and grep on filenames yourself.

Thanks for your suggestions. Unfortunately File::File etc won’t work as we don’t want to change several 1,000 file specs ( sorry if some of the restriction seem arbitrary, but there are good reasons for them)

In the end we decided to use the file spec to pull back a super set of what we wanted. We then converted any '*' into '(.*?)' and did a regex. If $1 contains a '+' then we exclude the file e.g.

my $spec = ‘*_{process,read}_*’;

my $reg = $spec;
$reg =~ s/\*/(.*?)/g;

my @use;
for my $file ( glob $spec )  {
    $file = m/$reg/;
    push @use, $file unless $1 =~ /\+/;
}
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Note: That’s a simplification of the code, which works, I haven’t tested or run the code above. It’s just for illustration here.

I suppose in the end it was a PERL question after all.

Thanks for your suggestions. Unfortunately File::File etc won’t work as we don’t want to change several 1,000 file specs ( sorry if some of the restriction seem arbitrary, but there are good reasons for them)

To be fair I don't understand your concerns since I don't have the slightest idea about what you mean with "to change several 1,000 file specs". I suspect that you, in turn, did misunderstood the suggestion about File::Find.

my $spec = ‘*_{process,read}_*’;
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Please use real single quotes: what are you using as an editor?!?

my @use;
for my $file ( glob $spec )  {
    $file = m/$reg/;
    push @use, $file unless $1 =~ /\+/;
}
[download]

This won't work, since since {process,read} does not do what you seem to think it does, in a regex. You probably want

my @use=grep !/[^+]*?_(?:process|read)_/, glob $spec;
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But then you should be aware that you're duplicating your efforts, performing two very similar pattern matches one after the other. Although I'm a big advocate of glob whereas I often see people do unnecessary opendirs and readdirs, in this case I feel like suggesting you to follow that path...

I suppose in the end it was a PERL question after all.

No, it was not a "PERL" question, since there's not such a thing. Check

perldoc -q 'difference between "perl" and "Perl"'
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and while you're there, PERL as shibboleth and the Perl community.