william nelson wrote in post #992087:
> I am trying to execute the Sudoku Solver listed in the book "The Ruby
> Programming Book" (pages 17 -24)
>
> The code for the Sudoku Module is available online but I do not
> understand the following instruction:
>
> require 'sudoku'
> puts Sudoku.solver(Sudoku::Puzzle.new(ARGF.readlines))
>
> Can someone walk me through (baby-steps) how to actually "require"
> sudoku so that I can see the Module in action. The more explicit your
> answer the better since I am a newbee's newbee!

When you require() a file, ruby looks in some default directories for 
the file.  You can see which directories are searched by default like 
this:

puts $LOAD_PATH

The default directoies that are displayed should also include the 
current directory ("."), which is the directory specified in the prompt 
next to which your typed the command to run your program:

some_dir/sub_dir> ruby my_program.rb

So if the file you are trying to include is in the current directory, or 
one of the default directories, you can require() it.

If the file you are trying to require() is in some other directory, then 
you need to either move it into the current directory or one of the 
default directories; or you can tell ruby to also search the directory 
which contains the file you are trying to require().

There are several ways to accomplish that:

1) Add the directory containing the file you want to require() to the 
directories that are searched by default:

$LOAD_PATH << "/some_dir/sub_dir/my_ruby_programs/"

For a more permanent solution, you can also:

2) Add the directory containing the file you want to require, to your 
system's PATH environment variable.

3) Create a new environment variable called RUBYPATH, which specifies 
additional directories that you want ruby to search.

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