what is -w and -T in perl

The #! is commonly called a "shebang" and it tells the computer how to run a script. You'll also see lots of shell-scripts with #!/bin/sh or #!/bin/bash.
So, /usr/bin/perl is your Perl interpreter and it is run and given the file to execute.

The rest of the line are options for Perl.
#!/usr/bin/perl is called shebang line. 

-w for warnings-
When you add -w you're asking the Perl compiler to warn you about things in your code that may be errors.

-T for Taint mode-
it means input is marked as "not trusted" until you check it's format.