When you get a slew of errors and warnings all mixed together, you can reduce the clutter by disabling the warnings on the command line using -X option:

P:\test>type junk.pl
#! perl -slw
use strict;

my( $a, @b, %c );

if 1 ) {
        my( $a, @b, %c );
}

P:\test>perl -c junk.pl
"my" variable $a masks earlier declaration in same scope at junk.pl li
+ne 8.
"my" variable @b masks earlier declaration in same scope at junk.pl li
+ne 8.
"my" variable %c masks earlier declaration in same scope at junk.pl li
+ne 8.
syntax error at junk.pl line 7, near "if 1"
junk.pl had compilation errors.

P:\test>perl -Xc junk.pl
syntax error at junk.pl line 7, near "if 1"
junk.pl had compilation errors.
[download]

This even seems to disable use warnings which is nice.