$ nl -ba foo.pl
     1  #!/usr/bin/perl
     2  use strict;
     3  use warnings;
     4
     5  my $x;
     6  my $y;
     7
     8  $y = 42;
     9  print "$y\n";
    10


$ perl -MO=Xref foo.pl

File foo.pl
  Subroutine (definitions)
    Package Internals
      &HvREHASH         s0
      &SvREADONLY       s0
      &SvREFCNT         s0
      &hash_seed        s0
      &hv_clear_placeholders  s0
      &rehash_seed      s0
    Package PerlIO
      &get_layers       s0
    Package Regexp
      &DESTROY          s0
    Package UNIVERSAL
      &VERSION          s0
      &can              s0
      &isa              s0
  Subroutine (main)
    Package (lexical)
      $x                i5
      $y                i6, 8, 9
foo.pl syntax OK