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       -s   enables rudimentary switch parsing for switches on
            the command line after the program name but before
...

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

#!/usr/bin/perl -ws
# minus-ess.pl
...
my $switch = "hooray" unless (defined $switch);

print $switch;

Global symbol "$switch" requires explicit package name at minus-ess.pl
+ line 7.