On further investigation, it appears GrandFather's solution, as corrected by nmerriweather, is correct. ikegami's solution passes a 1 into @captures in the case of a successful match with no captures requested. This doesn't DWIM, and it proved to be a deal-breaker in my real-world task. 

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

print "\nIncorrect\n\n";

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

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$/, $l
+ine ) );

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$/, $li
+ne ) );

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"
+;
}

[download]

Jim Keenan

In reply to Re^4: regex question - dynamically address captures by jkeenan1
in thread regex question - dynamically address captures by nmerriweather

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