Ruby User's Guide

Strings

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

ruby> "abc"
   "abc"
ruby> 'abc'
   "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"
a
b
c
   nil
ruby> puts 'a\nb\n'
a\nb\nc
   nil
ruby> "\n"
   "\n"
ruby> '\n'
   "\\n"
ruby> "\001"
   "\001"
ruby> '\001'
   "\\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"
   "foobar"
ruby> "foo" * 2
   "foofoo"

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);
/* ... */
free(s);

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.

Concatenation:

ruby> word = "fo" + "o"
   "foo"

Repetition:

ruby> word = word * 2
   "foofoo"

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"
   "parsley"
ruby> herb[0,1]
   "p"
ruby> herb[-2,2]
   "ey"
ruby> herb[0..3]
   "pars"
ruby> herb[-5..-2]
   "rsle"

Testing for equality:

ruby> "foo" == "foo"
   true
ruby> "foo" == "bar"
   false

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
  guess.chop!
  if guess == secret
    puts "You win!"
    break
  else
    puts "Sorry, you lose."
  end
  print "guess? "
end
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) 2005-2008 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."