Use strict and warning

#!/usr/bin/perl

Today I read a perl script,I saw the "use strict" and "use warnings" in the head lines of content.

I learned about it's function and using method. ?I would write it here.

Put this line at the top of your script (after the shebang,e.g.,'#!/usr/bin/perl' line):

 
 

  
  use strict;
 
 

In version 5.6 or later you can put this right around the same place you put 'use strict;':

 
 

  
  use warnings;
 
 

In perl's before 5.6 (or if you just want to be portable between the versions),you can put '-w' on the 'shebang' line,or set the $^W variable (however,setting $^W will not catch compile time warnings unless its in a BEGIN{} block,so '-w' is usually preferable):

 
 

  
  #!/usr/local/bin/perl -w # Or $^W = 1; # Or BEGIN { $^W = 1 }
 
 

If you want to disable the warning in some limited scope.

1

sub add_two_numbers_which_might_be_undef?

{
?# See 'perldoc perllexwarn' for all the categories of warnings
?# because its better to only disable the warnings you're expecting
?no warnings "uninitialized";
?$_[0] + $_[1];
}

2
sub add_two_numbers_which_might_be_undef?

{?local $^W;?$_[0] + $_[1];}