perldoc perlrun:

    -s   enables rudimentary switch parsing for switches on the comman
+d line
         after the program name but before any filename arguments (or 
+before
         an argument of --). This means you can have switches with two
         leading dashes (--help). Any switch found there is removed fr
+om
         @ARGV and sets the corresponding variable in the Perl program
+. The
         following program prints "1" if the program is invoked with a
+ -xyz
         switch, and "abc" if it is invoked with -xyz=abc.

             #!/usr/bin/perl -s
             if ($xyz) { print "$xyz\n" }

         Do note that --help creates the variable ${-help}, which is n
+ot
         compliant with "strict refs".
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And that last note is noteworthy. Such variables are not the same as lexical variables; they are package variables in package main::.

-- Randal L. Schwartz, Perl hacker