interactive shell for ruby

eval.rb

#!/usr/local/bin/ruby

#######################################################
#
# Ruby interactive input/eval loop
# Written by matz           ([email protected])
# Modified by Mark Slagell  ([email protected])
#    with suggestions for improvement from Dave Thomas
#                           ([email protected])
#
#######################################################
#
# NOTE - this file has been renamed with a .txt extension to
# allow you to view or download it without the rubyist.net
# web server trying to run it as a CGI script.  You will
# probably want to rename it back to eval.rb.
#
#######################################################

module EvalWrapper

  # Constants for ANSI screen interaction.  Adjust to your liking.
  Norm = "\033[0m"
  PCol = Norm           # Prompt color
  Code = "\033[1;32m"   # yellow 
  Eval = "\033[0;36m"   # cyan 
  Prompt = PCol+"ruby> "+Norm
  PrMore = PCol+"    | "+Norm
  Ispace = "   "        # Adjust length of this for indentation.
  Wipe = "\033[A\033[K" # Move cursor up and erase line
  
  # Return a pair of indentation deltas. The first applies before
  # the current line is printed, the second after.
  def EvalWrapper.indentation( code )
    case code
    when /^\s*(class|module|def|if|case|while|for|begin)\b[^_]/
      [0,1]      # increase indentation because of keyword
    when /^\s*end\b[^_]/
      [-1,0]     # decrease because of end
    when /\{\s*(\|.*\|)?\s*$/
      [0,1]      # increase because of '{'
    when /^\s*\}/
      [-1,0]     # decrease because of '}'
    when /^\s*(rescue|ensure|elsif|else)\b[^_]/
      [-1,1]     # decrease for this line, then come back
    else
      [0,0]      # we see no reason to change anything
    end
  end
  
  # On exit, restore normal screen colors.
  END {  print Norm,"\n" }
  
  
  ##############################################################
  # Execution starts here.
  ##############################################################
  
  indent=0
  while TRUE   # Top of main loop.
    
    # Print prompt, move cursor to tentative indentation level, and get
    # a line of input from the user.
    if( indent == 0 )
      expr = ''; print Prompt  # (expecting a fresh expression)
    else
      print PrMore             # (appending to previous lines)
    end
    print Ispace * indent,Code
    line = gets
    print Norm
    
    if not line
      # end of input (^D) - if there is no expression, exit, else
      # reset cursor to the beginning of this line.
      if expr == '' then break else print "\r" end
    else
      
      # Append the input to whatever we had.
      expr << line
      
      # Determine changes in indentation, reposition this line if
      # necessary, and adjust indentation for the next prompt.
      begin
	ind1,ind2 = indentation( line )
	if( ind1 != 0 )
	  indent += ind1
	  print Wipe,PrMore,(Ispace*indent),Code,line,Norm
	end
	indent += ind2
      rescue      # On error, restart the main loop.
	print Eval,"ERR: Nesting violation\n",Norm
	indent = 0
	redo
      end
      
      # Okay, do we have something worth evaulating?
      if (indent == 0) && (expr.chop =~ /[^; \t\n\r\f]+/)
	begin
	  result = eval(expr, TOPLEVEL_BINDING).inspect
	  if $!  # no exception, but $! non-nil, means a warning
	    print Eval,$!,Norm,"\n"
	    $!=nil
	  end
	  print Eval,"   ",result,Norm,"\n"
	rescue ScriptError,StandardError
	  $! = 'exception raised' if not $!
	  print Eval,"ERR: ",$!,Norm,"\n"
	end
	break if not line
      end
    end
  end  # Bottom of main loop
  print "\n"

end