It makes no sense to check if the file exists when wild cards aren't present.

perl foo.pl --help           shouldn't become   perl foo.pl
perl foo.pl infile outfile   shouldn't become   perl foo.pl infile
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It makes no sense to not honour wild cards. If you ask for all files matching «foo.?», it makes no sense to return «foo.?» unless «foo.?» exists. If you want the glob to return «foo.?», you'd pass «foo.\?».

PS — Perl matches csh's behaviour. You tested using the wrong shell.