The flag is the bit OR of several valid values. For example, the flag can be set to MSG_PEEK, if you use that value with recv, recv() will only peek at the buffer, but will not remove data from the buffer:

use IO::Socket::INET;

use strict;
use warnings;

my $s = IO::Socket::INET->new(Proto=>"tcp", PeerAddr => "www.yahoo.com
+", PeerPort => 80);
print $s "GET / HTTP/1.1\r\nHost: www.yahoo.com\r\n\r\n";
my $foo;
for (1..5) {
    recv $s, $foo, 15, MSG_PEEK;
    print "========\n";
    print $foo;
    print "\n";
}
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If you run the above code, you will keep getting the first 15 bytes of the response:

========
HTTP/1.1 200 OK
========
HTTP/1.1 200 OK
========
HTTP/1.1 200 OK
========
HTTP/1.1 200 OK
========
HTTP/1.1 200 OK
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