Ruby User's Guide


Ruby deals with strings as well as numerical data. A string may be double-quoted ("...") or single-quoted ('...').

ruby> "abc"
ruby> 'abc'

Double- and single-quoting have different effects in some cases. A double-quoted string allows character escapes by a leading backslash, and the evaluation of embedded expressions using #{}. A single-quoted string does not do this interpreting; what you see is what you get. Examples:

ruby> puts "a\nb\nc"
ruby> puts 'a\nb\n'
ruby> "\n"
ruby> '\n'
ruby> "\001"
ruby> '\001'
ruby> "abcd #{5*3} efg"
   "abcd 15 efg"
ruby> var = " abc "
   " abc "
ruby> "1234#{var}5678"
   "1234 abc 5678"

Ruby's string handling is smarter and more intuitive than C's. For instance, you can concatenate strings with +, and repeat a string many times with *:

ruby> "foo" + "bar"
ruby> "foo" * 2

Concatenating strings is much more awkward in C because of the need for explicit memory management:

char *s = malloc(strlen(s1)+strlen(s2)+1);
strcpy(s, s1);
strcat(s, s2);
/* ... */

But using ruby, we do not have to consider the space occupied by a string. We are free from all memory management.

Here are some things you can do with strings.


ruby> word = "fo" + "o"


ruby> word = word * 2

Extracting characters (note that characters are integers in ruby):

ruby> word[0]
   102            # 102 is ASCII code of `f'
ruby> word[-1]
   111            # 111 is ASCII code of `o'

(Negative indices mean offsets from the end of a string, rather than the beginning.)

Extracting substrings:

ruby> herb = "parsley"
ruby> herb[0,1]
ruby> herb[-2,2]
ruby> herb[0..3]
ruby> herb[-5..-2]

Testing for equality:

ruby> "foo" == "foo"
ruby> "foo" == "bar"

Note: In ruby 1.0, results of the above are reported in uppercase, e.g. TRUE.

Now, let's put some of these features to use. This puzzle is "guess the word," but perhaps the word "puzzle" is too dignified for what is to follow ;-)

# save this as guess.rb
words = ['foobar', 'baz', 'quux']
secret = words[rand(3)]

print "guess? "
while guess = STDIN.gets
  if guess == secret
    puts "You win!"
    puts "Sorry, you lose."
  print "guess? "
puts "The word was ", secret, "."

For now, don't worry too much about the details of this code. Here is what a run of the puzzle program looks like.

% ruby guess.rb
guess? foobar
Sorry, you lose.
guess? quux
Sorry, you lose.
guess? ^D
The word was baz.

(I should have done a bit better, considering the 1/3 probability of success.)

Copyright (c) 2005 Mark Slagell

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.

A copy of the license is included in the section entitled "GNU Free Documentation License."