if ( $] >= 5.006 ) {
   print "This is good, your Perl is version $]\n";
}
else {
   warn "Your Perl is only version $]: Bad!";
}

##</code><code>##

require 5.006_001;  # check at run-time, at this point in code.
use 5.006_001;      # check at compile-time

##</code><code>##

eval {
   require 5.006_001;
};
if ($@) {  # $@ is set if the 'require' dies
   warn "Your Perl is too old."
   system ('n:\\install\\upgrade-perl.exe'); # imaginary
}

##</code><code>##

# import a version of a module at compile time, die on failure
use Module 1.02; # dies unless Module is at least v1.02

# at runtime, find version and act on it.
eval {
   require Module; # if not installed, dies (go to end of eval)
   if ($Module::VERSION >= 1.02) {
      print "Module version is OK\n";
   }
   else {
      warn "Module is installed, but is too old";
      # maybe upgrade it here
   }
}
if ($@) { # run if 'require Module' fails
   warn "Module is not available";
   # maybe install it here
}

##</code><code>##

if (-f 'c:\\program files\\some app\\app.exe') {
   print "APP is installed, good.\n";
}
else {
   warn "APP not installed!";
}