messages
messages.
messages.1
messages1.2.3
messages.1.gz
messages.2
messages.3
messages.pl
messages.txt

##</code><code>##

opendir D, '.';
while(readdir D) {
   /^messages(?:\.\d?)?$/ and print $_,"\n";
}

##</code><code>##

messages.
messages.2
messages
messages.1
messages.3

##</code><code>##

opendir D, '.';
while(readdir D) {
   m/            # begin of match
       ^         # match at the beginning of element, i.e. $_
       messages  # match 'messages' literally
       (         # begin of match group
        ?:       # subject to * ? +  not creating a capture
          \.     # match a period
          \d?    # optionally (?) match a digit
       )         # end of match group
       ?         # which may or not occur
       $         # before the end of the string
    /x           # tell m// that we use extended regex w/comments
    and          # if found
    print "$_\n" # print it out.
}