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Ruby Programming
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Using eruby

eruby acts as a filter, plain and simple. Any text within the input file is passed through untouched, with the following exceptions:

Expression Description
<% ruby code %> The Ruby code between the delimiters is replaced with its output.
<%= ruby expression %> The Ruby expression between the delimiters is replaced with its value.
<%# ruby code %> The Ruby code between the delimiters is ignored (useful for testing).

You invoke eruby as:

eruby [
            ] [

If the document is omitted, eruby will read from standard input. The command-line options for eruby are shown in Table 14.1 on page 149.
Command-line options for eruby
Option Description
-d, --debug Sets $DEBUG to true.
-K kcode Specifies an alternate coding system (see page 137).
-M mode Specifies runtime mode, one of:

f filter mode
c CGI mode (prints errors as HTML, sets $SAFE=1)
n NPH-CGI mode (prints extra HTTP headers, sets $SAFE=1)
-n, --noheader Disables CGI header output.
-v, --verbose Enables verbose mode.
--version Prints version information and exits.

Let's look at some simple examples. We'll run the eruby executable on the following input.

This text is <% a = 100; puts "#{a}% Live!" %>

eruby substitutes the expression between the delimiters and produces

This text is 100% Live!

Using the <%= form acts as if you printed the value of the expression. For instance, the input

<%a = 100%>This text is almost <%=a%> degrees! Cool!

replaces the =a with the value of a.

This text is almost 100 degrees! Cool!

And, of course, you can embed Ruby within a more complex document type, such as HTML.

<title>eruby example</title>
<%(1..10).each do|i|%>
  <li>number <%=i%></li>
<h1>Environment variables</h1>
<%ENV.keys.sort.each do |key|%>
Ruby Programming
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