use strict;
use warnings;

my $re = qr/
    \{ # Opening bracket
    ((?: # Capture the contents
        [^}{]+
        |
        (??{$re}) # Or recurse
    )+) # and allow repeats internally
    \} # Closing bracket
    /x;

my $str = do { local $/; <DATA> };

while ($str =~ /sub\s+(.*?)\s*?$re/gsi) {
    print "Subroutine [$1]\n",
          "=================\n",
          "{$2}\n\n";
}

__DATA__

sub max
{
    my ($a, $b) = @_;
    return $a > $b ? $a : $b;
}

sub min {
    my ($a, $b) = @_;
    return $a < $b ? $a : $b;
}