void      $scalar            @array        %hash
 scalar    @array             @array[0, 2]                 
 list      %hash                               
           &sub
                    
                    number, string, reference,       undef

 \     references      
 $@%&  dereference     
 []    anon. arrayref  
 {}    anon. hashref   
 \()   list of refs
                         
                         =          =        perl.plover.com
                         +                   search.cpan.org
 ++ --                   == !=      eq ne         cpan.org
 **                      < > <= >=  lt gt le ge   pm.org
 !   \ u+ u-             <=>        cmp           tpj.com
    !~                                            perldoc.com
 * / % x                 
 + - .                   for    (LIST) { }, 
                         while  ( ) { }, until ( ) { }
 named uops              if     ( ) { } elsif ( ) { } else { }
 < > <= >= lt gt le ge   unless ( ) { } elsif ( ) { } else { }
 == != <=> eq ne cmp     
  
                  
 &&               ^     string begin      
 ||                                      
 ..               +     one or more     
                  *     zero or more   
 = += -= *= etc.  ?     zero or one    
 ,                                  
 list ops         ()    capture          
 not                                                  
 and                                     \s == [\x20\f\t\r\n]
 or xor           |     alternation      \w == [A-Za-z0-9_]
                  \b    word boundary    \d == [0-9] 
                                         \S, \W and \D negate

 use strict;        
 use warnings;      "$foo"           perl.com       
 my $var;           $$variable_name  perlmonks.org  
 open() or die $!;  `$userinput`     use.perl.org   
 use Modules;       /$userinput/     perl.apache.org
                                     parrotcode.org 

 stat      localtime    caller         
  0 dev    0 second     0 package      $_    default variable
  1 ino    1 minute     1 filename     
  2 mode   2 hour       2 line         
  3 nlink  3 day        3 subroutine   
  4 uid    4 month-1    4 hasargs      
  5 gid    5 year-1900  5 wantarray    
  6 rdev   6 weekday    6 evaltext     
  7 size   7 yearday    7 is_require   
  8 atime  8 is_dst     8 hints        
  9 mtime               9 bitmask      @ARGV command line args
 10 ctime  just use                    @INC  include paths
 11 blksz  POSIX::      3..9 only      @_    subroutine args
 12 blcks  strftime!    with EXPR      %ENV  environment