in the elemetns of programming perl , I need help with 2 lines that I don't understand

In the book "elements of programming perl", below program is presented.

I don't really understand these 2 lines. can someone break it down for 
me please?

$pattern = '.*(?:' . join('|', @ARGV) . ')';

$pattern = join('', map{"(?=.*$_)"} @ARGV);


#!/usr/bin/perl


use strict;
use warnings;

my $faqdir = '/usr/lib/perl5/5.10.0/pod/';
my($opt_f,$opt_or,$pattern);

die "no keywords specified\n" unless @ARGV;

while ( $ARGV[0] =~ /^-/ ) {
     $_ = $ARGV[0];
     if ( /^-or$/ ) { $opt_or = 1; shift @ARGV; next }
     if ( /^-f$/  ) { $opt_f  = 1; shift @ARGV; next }
die<<HERE;
illegal option: $_
usage: faqgrep [-f] [-or] [keywords...]
HERE
}

if ( $opt_or) {
     $pattern = '.*(?:' . join('|', @ARGV) . ')';
} else {
     $pattern = join('', map{"(?=.*$_)"} @ARGV);
}
opendir(FAQDIR,$faqdir) or die "can't open $faqdir $!";
my @faqs = grep /faq/, readdir FAQDIR;
closedir FAQDIR;

foreach my $faq ( @faqs ) {
    open ( FAQ, "$faqdir/$faq" ) or die "can't $!";
    while ( <FAQ> ) {
        if (s/^=head2($pattern)/$1/io) {
             print "$faq:$_";
             if ( $opt_f ) {
                   while ( <FAQ> ) {
                       last if m/^=head(?!$pattern)/io;
                       print;
                   }
             }
        }
    }
}