#!/usr/bin/perl -w
use Fcntl qw(LOCK_EX);

# instrument LOCK_EX
my $lock_ex_coderef = \&Fcntl::LOCK_EX;
*Fcntl::LOCK_EX = sub { 
    print "LOCK_EX called\n";
    return &$lock_ex_coderef; 
};

# call LOCK_EX
$_ = LOCK_EX;