You can create string literals in Ruby using either single or double quotes.

You can do a little bit more with double quoted strings. E.g., you can insert arbitrary Ruby expressions using string interpolation.

> "360 degrees=
#{2*Math::PI} radians"
=> "360 degrees=6.283185307179586 radians"

If you enclose a string in single backquotes (backticks), the string will be executed as a command in the underlying OS.

> ‘date‘
=> "Tue Oct 15 09:10:21 MDT 2013\n"

Strings in Ruby are mutable, as in C/C++, but unlike Java. Thus, each time Ruby encounters a new string literal, it create a new String object. I.e, if you’re creating a string literal within a loop, each iteration will create a new String object.

The Ruby String class contains a number of methods which can be used to manipulate strings.

> name = "Homer Blimpson"  # => "Homer Blimpson"
> name.length            # => 14
> name[6]                # => "B"
> name[6..14]            # => "Blimpson"
> "Bart " + name[6..14]    # => "Bart Blimpson"
> name.encoding      # =>   <encoding:utf-8>

Regular Expression Class

Ruby has a regular expression class, called Regexp, that is closely related to strings.

A regular expression provides a concise and flexible means for matching strings of text, such as particular characters, words, or patterns of characters.

In Ruby, a regular expression is written in the form of:

where “pattern” is the regular expression itself, and “modifiers” are a series of characters indicating various options. The “modifiers” part is optional. This syntax is borrowed from Perl.

To test if a particular Regex matches (part of) a string, use the =∼ operator. This operator returns the character position in the string of the start of the match (which evaluates to true in a boolean test), or nil if no match was found (which evaluates to false).

"Homer" =~ /er/     # => 3

Regular Expressions

The following have special meanings in patterns:

[ ]range specification, e.g., [a-z] means a letter between a and z
\w word character, same as [0-9A-Za-z_]
\W non-word character
\s space character, same as [\t\n\r\f]
\S non-space character
\d digit character, same as [0-9]
\D non-digit character
\b backspace (if used in a range specification)
\b word boundary (if not used in a range specification)
\B non-word boundary
* zero or more repetitions of the preceding
+ one or more repetitions of the preceding
{m,n}at least m and at most n repetitions of the preceding
? at most one repetition of the preceding, same as {0,1}
| either preceding or next expression may match
( )grouping

The preceding table only contained a partial list of the special characters that can be used in a Ruby regular expression. Consult a Ruby reference for more details.

Regular expression are often used to process strings.
Ex. The following Ruby expression will replace all of the non-digit characters in phone with "". I.e., it will strip everything out of the phone number, except digits:

phone = phone.gsub!(/\D/, "")

Regular expression are commonly used to validate emails, phone numbers, and other user-supplied input.
Ex. The following regular expression can be used to validate email addresses:

(Note: We didn’t cover all of the characters used in this regular expression.)


Ruby symbols are also closely related to strings.

A Ruby interpreter maintains a symbol table where it stores the names of all classes, methods and variables.

You can add your own symbols to this table. Specifically, a symbol is created if you precede a name with a colon. Ex. attr_reader :row, :col

Ruby symbols are used to represent names and strings; however unlike

String objects, symbols of the same name are initialized and exist in memory only once during a Ruby session.

Ruby symbols are immutable, and cannot be modified during runtime. Ex. :name = "Homer" # => will yield an error

There’s a big space advantage associated with symbols, as each unique is only stored once in memory. Multiple strings with the same name my exist in memory.

> puts :name.object_id # => yields 20488
> puts :name.object_id # => yields 20488
> puts "name".object_id # => yields 2168472820
> puts "name".object_id # => yields 2168484060

When should you use a string and when should you use a symbol? General rules of thumb:

  • – If the contents (i.e., the sequence of characters) of the object is important, e.g., if you need to manipulate these characters, use a string.
  • – If the identity of the object is important (in which case you probably don’t want to manipulate the characters), use a symbol