my $line = q{Convention_9841_12345678901234.txt};
my @captures;

print "\nIncorrect\n\n";

print_captures( incorrect( qr/Convention_(\d{4})_(\d{14})\.txt$/, $line ) );

print_captures( incorrect( qr/Convention_(\d{4})_\d{14}\.txt$/, $line ) );

print_captures( incorrect( qr/Convention_\d{4}_\d{14}\.txt$/, $line ) );

print_captures( incorrect( qr/Convention_((\d{4})_(\d{14}))\.txt$/, $line ) );

print_captures( incorrect( qr/^(.*Convention_(\d{4})_(\d{14})\.txt)$/, $line ) );
print "\nCorrect\n\n";
print_captures( get_captures( qr/Convention_(\d{4})_(\d{14})\.txt$/, $line ) );

print_captures( get_captures( qr/Convention_(\d{4})_\d{14}\.txt$/, $line ) );

print_captures( get_captures( qr/Convention_\d{4}_\d{14}\.txt$/, $line ) );

print_captures( get_captures( qr/Convention_((\d{4})_(\d{14}))\.txt$/, $line ) );

print_captures( get_captures( qr/^(.*Convention_(\d{4})_(\d{14})\.txt)$/, $line ) );

sub incorrect {
    my ($pattern, $line) = @_;
    my @captures;
    (@captures) = $line =~ m/$pattern/ or return;
    return @captures;
}

sub get_captures {
    my ($pattern, $line) = @_;
    $line =~ m/$pattern/ or return;
    return map {substr $line, $-[$_], $+[$_] - $-[$_]} (1 .. $#-);
}

sub print_captures {
    my @captures = @_;
    @captures ? print "captures:  @captures\n" : print "no captures\n";
}