The -w option passed to the perl command generates a warning about the code itself.

  
#!/usr/bin/perl -w

# Test of open and die with $!.

$filename = "nofile";

open(TMP, $filename) or die "Can't open \"$filename\" due to $! ";

1.	A program that uses the -0 option.
2.	A program that uses the -l option.
3.	Edit files using the -i option.
4.	The -c Switch checks the Perl syntax without actually executing the Perl commands
5.	The -e switch executes Perl statements at the command line instead of from a script.
6.	The -n Switch: print the contents of a file or search for a line that contains a particular pattern
7.	Using -e option to execute the perl statement
8.	Using /e modifier to evaluate
9.	Using the -n option.
10.	Using two statements with -e option
11.	Using variable with -e option
12.	'#!/usr/bin/perl -w ' tells the perl command to turn on extra warnings with the -w option.
13.	An example of the -a option.
14.	Perl can take its input from a file and send its output to a file using standard I/O redirection.
15.	Executing the Script

The -w option passed to the perl command generates a warning about the code itself. : Perl Command « Language Basics « Perl