An identifier is a name used to identify a variable, method, or class.
As with most languages, valid identifiers consist of alphanumeric characters (A-Za-z0-9) and underscores (_), but may not begin with a digit (0-9). Additionally, identifiers that are method names may end with a question mark (?), exclamation point (!), or equals sign (=).
There are no arbitrary restrictions to the length of an identifier (i.e. it may be as long as you like, limited only by your computer's memory). Finally, there are reserved words which may not be used as identifiers.
Line comments run from a bare '#' character to the end of the line. Code commenting and documentation is best implemented with Ruby Embedded Documentation. http://www.ruby-doc.org/docs/ProgrammingRuby/html/rdtool.html
# this line does nothing; print "Hello" # this line prints "Hello"
=begin Everything between a line beginning with `=begin' down to one beginning with `=end' will be skipped by the interpreter. These reserved words must begin in column 1. =end
The following words are reserved in Ruby:
__FILE__ and def end in or self unless __LINE__ begin defined? ensure module redo super until BEGIN break do false next rescue then when END case else for nil retry true while alias class elsif if not return undef yield
You can find some examples of using them here.
true (1 + 2) * 3 foo() if test then okay else not_good end
All variables, literals, control structures, etcetera are expressions. Using these together is called a program. You can divide expressions with newlines or semicolons (;) — however, a newline with a preceding backslash (\) is continued to the following line.
Since in Ruby control structures are expressions as well, one can do the following:
foo = case 1 when 1 true else false end
The above equivalent in a language such as C would generate a syntax error since control structures are not expressions in the C language.