Programming Perl, 4th Edition

Pragmas

Many programming languages allow you to give hints to the compiler. In Perl, these hints are conveyed to the compiler with the use declaration. Some pragmas are:

use warnings;
use strict;
use integer;
use bytes;
use constant pi => ( 4 * atan2(1,1) );

Perl pragmas are all described in Chapter 29, but right now we’ll just talk specifically about a couple that are most useful with the material covered in this chapter.

Although a few pragmas are global declarations that affect global variables or the current package, most are lexically scoped declarations whose effects are constrained to last only until the end of the enclosing block, file, or eval (whichever comes first). A lexically scoped pragma can be countermanded in an inner scope with a no declaration, which works just like use but in reverse.