A easy example to tell you what is "2>&1" in Perl

You can decide if make the output shown on command screen by using 2>&1 or NUL

Testing script:

print "without null ";

system("dir 2>&1");

print "with null ";

system("dir > NUL");

print "end ";

Result:

C:RebeccascriptperlUnicode>perl calculate.pl

without null

 Volume in drive C isOSDisk

 Volume Serial Numberis BA23⑸612

 Directory of C:RebeccascriptperlUnicode

01/22/2015  04:59PM    <DIR>          .

01/22/2015  04:59PM    <DIR>          ..

01/22/2015  04:58PM               227 calculate.pl

01/22/2015  09:19AM               194 unicode_test_v1.pl

01/21/2015  05:23PM               193unicode_test_v1.pl.ba

               3File(s)            614 bytes

               2Dir(s)  175,476,535,296 bytes free

with null   #you can see with NUL, there isn't any output shown here

end