Why it is important to turn it on ?
Perl is very forgiving of strange and sometimes wrong code, which can mean hours spent searching for bugs and weird results. Turning on warnings helps uncover common mistakes and strange places and save a lot of debugging time in the long run.
There are various ways of turning on Perl warnings:
For Perl one-liner, use -w option on the command line.
On Unix or Windows, use the -w option in the shebang line (The first # line in the script). Note: Windows Perl interpreter may not require it.
For other systems, choose compiler warnings, or check compiler documentation.
You can turn it off with following keyword. Will give you an example.
To explicitly turn off a "FATAL" warning you just disable the warning it is associated with. So, for example, to disable the "void" warning in the example above, either of these will do the trick:
no warnings qw(void);
no warnings FATAL => qw(void);