You may find this "revision table" useful if you've got a complex looking series of {}s, @s %s and $s in a piece of code you've been given to maintain!

1. Perl variables are dynamically created as your program runs.
  $abc         a scalar - holds a single number, string or reference
  @abc         a list - holds a collection of scalars indexed by position number
  %abc         a hash - holds a collection of scalars indexed by an scalar key of programmer's choice
  abc          a file handle - used for a set of buffers / interface to file system
  &abc         code - holds a named block of code - i.e. a sub
  *abc         a typeglob - a scalar, a hash, a list, a code and a file handle all of the same name

2. If you're referrring to an individual scalar member of a collection, you use the $ prefix and you use
  square bracket subscript           to indicate a member of a list
  curly brace subscript              to indicate a member of a hash

3. If you preceed a variable name, you can reference and dereference. Thus:
  \            means "A reference to"  or "the address of" if you prefer
  $            means "contents of" or "refers to"
  ->           an alternative notation for $
               example -  $$abc[3] and $abc->[3] mean the same thing
 
4. You can create anonymous lists and hashes
  $abc = {"England", "London", "Wales","Cardiff"}    creates an anonymous hash with two pairs
  $abc = {England => "London", Wales => "Cardiff"}   alternative notation
  $abc = ["England", "London", "Wales","Cardiff"]    creates an anonymous list with 4 members
  $abc = ("England", "London", "Wales","Cardiff")    probably WRONG - $abc takes the value "4".

5. If you refer to a list in a scalar context, you'll get the number of elements in the list.
If you refer to $#listname, you'll get the index number of the last element in the list.

6. You can also use {} to delimit a variable name - thus
  "$abkgs"     means a string containing the contents of the variable $abkgs
  "${ab}kgs"   means a string containing the contents of the variable $ab followed by "kgs"

7. You are limited only by your own ingenuity as to how complex a structure / expression you can make up using the above; I suggest that you use an Object Oriented design is you're looking at a really complex problem as this helps divide the code and complexity down into a series of different parts each of which can be developed and tested before you move on to the next stage.

Here's some sample (demo) code using most of the things I described in the previous post - can you work them out??

Code:

$var = "Hello"; $itsat = \$var;     # reference to a scalar print $var,"\n"; print $itsat ,"\n"; print $$itsat ,"\n\n";   # contents of @stuff = ("tom","dick","arry"); $itsat = \@stuff;     # reference to a list print @stuff,"\n";      # no separator print "@stuff\n";       # space separator print @stuff+0,"\n\n";  # scalar content - length of list print $itsat,"\n"; print @$itsat,"\n";     # list referenced by scalar print @{${itsat}},"\n\n";       # list referenced by scalar print $$itsat[2],"\n";  # element of list pointed to by a scalar print $itsat->[2],"\n"; # element of list pointed to by a scalar print $itsat->[-1],"\n\n";      # element of list pointed to by a scalar %table = ("Chris" , "S&Kpie", "Paul" , "Burger"); %table = (Chris => "S&Kpie", Paul => "Burger");  # alternative $itsat = \%table; print $itsat,"\n"; print %$itsat,"\n";     # hash referenced by scalar print %{${itsat}},"\n\n";       # hash referenced by scalar print $$itsat{"Chris"},"\n";    # element of list pointed to by a scalar print $itsat->{"Chris"},"\n";   # element of list pointed to by a scalar print $itsat->{"Chris"},"\n\n"; # element of list pointed to by a scalar $itsat = {"Carine","Pastie","Pali","Haddock"};  # ref to an anonymous hash print $itsat,"\n"; print %$itsat,"\n";     # hash referenced by scalar print %{${itsat}},"\n\n";       # hash referenced by scalar print $itsat->{"Carine"},"\n"; print $$itsat{"Carine"},"\n"; print ${${itsat}}{"Carine"},"\n"; $itsat = ["Lancashire","Yourkshire","Elsewhere"]; # ref to an anon list                # ( ) would give "3"! print $itsat,"\n"; print @$itsat,"\n";     # list referenced by scalar print @{${itsat}},"\n\n";       # list referenced by scalar print $$itsat[2],"\n";  # element of list pointed to by a scalar print $itsat->[2],"\n"; # element of list pointed to by a scalar print $itsat->[-1],"\n\n";      # element of list pointed to by a scalar $yikes = [{"Tom" => "Plumber", "Dick" => "Copper"},        {Carine => "Programmer", "Paul" => "Programmer"},        {Pali => "Hard Worker"}]; print "$yikes\n"; foreach $el (@$yikes) {        print "$el\n";                foreach $k (keys %$el) {                        print ("$k $$el{$k}\n");                }        }

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