问题
I am attempting to parse, not evaluate, rails ERB files in a Hpricot/Nokogiri type manner. The files I am attempting to parse contain HTML fragments intermixed with dynamic content generated using ERB (standard rails view files) I am looking for a library that will not only parse the surrounding content, much the way that Hpricot or Nokogiri will but will also treat the ERB symbols, <%, <%= etc, as though they were html/xml tags.
Ideally I would get back a DOM like structure where the <%, <%= etc symbols would be included as their own node types.
I know that it is possible to hack something together using regular expressions but I was looking for something a bit more reliable as I am developing a tool that I need to run on a very large view code base where both the html content and the erb content are important.
For example, content such as:
blah blah blah <div>My Great Text <%= my_dynamic_expression %></div>
Would return a tree structure like:
root
- text_node (blah blah blah)
- element (div)
- text_node (My Great Text )
- erb_node (<%=)
回答1:
I eventually ended up solving this problem by using RLex, http://raa.ruby-lang.org/project/ruby-lex/, the ruby version of lex with the following grammer:
%{
#define NUM 257
#define OPTOK 258
#define IDENT 259
#define OPETOK 260
#define CLSTOK 261
#define CLTOK 262
#define FLOAT 263
#define FIXNUM 264
#define WORD 265
#define STRING_DOUBLE_QUOTE 266
#define STRING_SINGLE_QUOTE 267
#define TAG_START 268
#define TAG_END 269
#define TAG_SELF_CONTAINED 270
#define ERB_BLOCK_START 271
#define ERB_BLOCK_END 272
#define ERB_STRING_START 273
#define ERB_STRING_END 274
#define TAG_NO_TEXT_START 275
#define TAG_NO_TEXT_END 276
#define WHITE_SPACE 277
%}
digit [0-9]
blank [ ]
letter [A-Za-z]
name1 [A-Za-z_]
name2 [A-Za-z_0-9]
valid_tag_character [A-Za-z0-9"'=@_():/ ]
ignore_tags style|script
%%
{blank}+"\n" { return [ WHITE_SPACE, yytext ] }
"\n"{blank}+ { return [ WHITE_SPACE, yytext ] }
{blank}+"\n"{blank}+ { return [ WHITE_SPACE, yytext ] }
"\r" { return [ WHITE_SPACE, yytext ] }
"\n" { return[ yytext[0], yytext[0..0] ] };
"\t" { return[ yytext[0], yytext[0..0] ] };
^{blank}+ { return [ WHITE_SPACE, yytext ] }
{blank}+$ { return [ WHITE_SPACE, yytext ] };
"" { return [ TAG_NO_TEXT_START, yytext ] }
"" { return [ TAG_NO_TEXT_END, yytext ] }
"" { return [ TAG_SELF_CONTAINED, yytext ] }
"" { return [ TAG_SELF_CONTAINED, yytext ] }
"" { return [ TAG_START, yytext ] }
"" { return [ TAG_END, yytext ] }
"" { return [ ERB_BLOCK_END, yytext ] }
"" { return [ ERB_STRING_END, yytext ] }
{letter}+ { return [ WORD, yytext ] }
\".*\" { return [ STRING_DOUBLE_QUOTE, yytext ] }
'.*' { return [ STRING_SINGLE_QUOTE, yytext ] }
. { return [ yytext[0], yytext[0..0] ] }
%%
This is not a complete grammer but for my purposes, locating and re-emitting text, it worked. I combined that grammer with this small piece of code:
text_handler = MakeYourOwnCallbackHandler.new
l = Erblex.new
l.yyin = File.open(file_name, "r")
loop do
a,v = l.yylex
break if a == 0
if( a < WORD )
text_handler.character( v.to_s, a )
else
case a
when WORD
text_handler.text( v.to_s )
when TAG_START
text_handler.start_tag( v.to_s )
when TAG_END
text_handler.end_tag( v.to_s )
when WHITESPACE
text_handler.white_space( v.to_s )
when ERB_BLOCK_START
text_handler.erb_block_start( v.to_s )
when ERB_BLOCK_END
text_handler.erb_block_end( v.to_s )
when ERB_STRING_START
text_handler.erb_string_start( v.to_s )
when ERB_STRING_END
self.text_handler.erb_string_end( v.to_s )
when TAG_NO_TEXT_START
text_handler.ignorable_tag_start( v.to_s )
when TAG_NO_TEXT_END
text_handler.ignorable_tag_end( v.to_s )
when STRING_DOUBLE_QUOTE
text_handler.string_double_quote( v.to_s )
when STRING_SINGLE_QUOTE
text_handler.string_single_quote( v.to_s )
when TAG_SELF_CONTAINED
text_handler.tag_self_contained( v.to_s )
end
end
end
回答2:
I recently had a similar problem. The approach that I took was to write a small script (erblint.rb) do a string substitution to convert the ERB tags (<% %> and <%= %>) to XML tags, and then parse using Nokogiri.
See the following code to see what I mean:
#!/usr/bin/env ruby
require 'rubygems'
require 'nokogiri'
# This is a simple program that reads in a Ruby ERB file, and parses
# it as an XHTML file. Specifically, it makes a decent attempt at
# converting the ERB tags (<% %> and <%= %>) to XML tags (<erb-disp/>
# and <erb-eval/> respectively.
#
# Once the document has been parsed, it will be validated and any
# error messages will be displayed.
#
# More complex option and error handling is left as an exercise to the user.
abort 'Usage: erb.rb <filename>' if ARGV.empty?
filename = ARGV[0]
begin
doc = ""
File.open(filename) do |file|
puts "\n*** Parsing #{filename} ***\n\n"
file.read(nil, s = "")
# Substitute the standard ERB tags to convert them to XML tags
# <%= ... %> for <erb-disp> ... </erb-disp>
# <% ... %> for <erb-eval> ... </erb-eval>
#
# Note that this won't work for more complex expressions such as:
# <a href=<% @some_object.generate_url -%> >link text</a>
# Of course, this is not great style, anyway...
s.gsub!(/<%=(.+?)%>/m, '<erb-disp>\1</erb-disp>')
s.gsub!(/<%(.+?)%>/m, '<erb-eval>\1</erb-eval>')
doc = Nokogiri::XML(s) do |config|
# put more config options here if required
# config.strict
end
end
puts doc.to_xhtml(:indent => 2, :encoding => 'UTF-8')
puts "Huzzah, no errors!" if doc.errors.empty?
# Otherwise, print each error message
doc.errors.each { |e| puts "Error at line #{e.line}: #{e}" }
rescue
puts "Oops! Cannot open #{filename}"
end
I've posted this as a gist on Github: https://gist.github.com/787145
来源：https://stackoverflow.com/questions/2588967/library-to-parse-erb-files