my $regex = join '|', map "\Q$_\E?", @filelist;
                  ^         ^ ^ ^^
                  |         | | ||
                  |         | | |+ - Last character in file name optional, i.e., the "l" in html
                  |         | | + - End quote metacharacters
                  |         | + - The default scalar aliased to each @filelist element
                  |         + - Begin quote metacharacters (e.g., the period)
                  + - Join each element with alternation ("or") character

##</code><code>##

1234567_3a_20101000\.html?|99877_b_20111111\.html?|99877_c_20111111\.html? ...

##</code><code>##

->name(qr/^(?:$regex)$/)
          ^^^^^^^^^^^^

##</code><code>##

my @matchingFileNames = grep /pattern/, @found_html;