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;
}
}
}
}
}
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