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First, you'll want to check whether ruby is installed. From the shell prompt (denoted here by "%", so don't type the %), type

% ruby -v

(-v tells the interpreter to print the version of ruby), then press the Enter key. If ruby is installed, you will see a message something like the following:

% ruby -v
ruby 1.6.6 (2001-12-26) [i586-linux]

If ruby is not installed, you can ask your administrator to install it, or you can do it yourself , since ruby is free software with no restrictions on its installation or use.

Now, let's play with ruby. You can place a ruby program directly on the command line using the -e option:

% ruby -e 'print "hello world\n"'
hello world

More conventionally, a ruby program can be stored in a file.

% cat > test.rb
print "hello world\n"
^D
% cat test.rb
print "hello world\n"
% ruby test.rb
hello world

^D is control-D. The above is just for UNIX. If you're using DOS, try this:

C:\ruby> copy con: test.rb
print "hello world\n"
^Z
C:\ruby> type test.rb
print "hello world\n"
C:\ruby> ruby test.rb
hello world

When writing more substantial code than this, you will want to use a real text editor!

Some surprisingly complex and useful things can be done with miniature programs that fit in a command line. For example, this one replaces foo with bar in all C source and header files in the current working directory, backing up the original files with ".bak" appended:

% ruby -i.bak -pe 'sub "foo", "bar"' *.[ch]

This program works like the UNIX cat command (but works slower than cat):

% ruby -pe 0 file

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