fruby

   1 #!/usr/bin/ruby
   2
   3 # (c) 2008 B. Crowell, GPL v 2
   4
   5 # This is designed to be more or less a drop-in replacement for eruby. It supports a subset
   6 # of eruby, and has better error handling.
   7 # Usage:
   8 #   fruby infile >outfile
   9 # How it's different:
  10 #   - Better error handling.
  11 #   - Parses and evaluates the input file on the fly, rather than
  12 #     translating it into a .rb file.
  13 #   - Supports <% %>, <%= %>, and <%# %>, but not % at beginning of line. This makes
  14 #     it compatible with TeX.
  15 #   - Doesn't support this kind of thing:
  16 #       <% 3.times do %> rah <% end %>
  17 #       <% if foo %> foo <% end %>
  18 #     Every block has to be a syntactically self-contained piece of ruby code.
  19 #     Variables assigned to in one piece of code *are* available in later pieces of code.
  20 #     This type of thing has to be accomplished by using a single block of ruby code,
  21 #     with print statements inside it.
  22 # Bugs:
  23 #   - Doesn't check if <% and %> are properly matched.
  24 # Security:
  25 #   Will happily run any code in the file.
  26
  27 def die(message)
  28   $stderr.print "fruby: " + message + "\n"
  29   exit(-1)
  30 end
  31
  32 # The following dummy subroutine is the environment in which we evaluate the code.
  33 # see pickaxe book, pp. 296, 419
  34 # This accomplishes two things for us:
  35 # - If we change a variable in one <% %> block, the change persists in later blocks.
  36 # - Local variables in <% %> blocks are separate from local variables in this program.
  37 def binding_for_eval()
  38   return binding()
  39 end
  40
  41 if ARGV.empty? then die("Usage: fruby infile >outfile") end
  42 infile = ARGV[0]
  43 if ! File.exist?(infile) then die("File #{infile} does not exist.") end
  44 t = nil
  45 File.open(infile,'r') { |f|
  46   t = f.gets(nil) # nil means read whole file
  47 }
  48
  49 b = binding_for_eval()
  50 inside = false # even if there is a ruby expression at the very beginning of the string, split() gives us a null string as our first string
  51 line = 1
  52 t.split(/(?:\<\%|\%\>)/).each { |x|
  53   if inside then
  54     what = 'execute'
  55     if x=~/\A=/ then what='evaluate' end
  56     if x=~/\A#/ then what='comment' end
  57     x.gsub!(/\A[=#]/,'')
  58     if what != 'comment' then
  59       y = eval(x,b,infile,line)
  60       if what == 'evaluate' then print y end
  61     end
  62   else
  63     print x
  64   end
  65   x.scan(/\n/) {line += 1}
  66   inside = !inside
  67 }