From: Wybo Dekker <wybo@...>
Date: 2005-06-18T05:37:58+09:00
Subject: Re: stubborn program using readline - Perl finally beaten

On Sat, 18 Jun 2005, Ara.T.Howard wrote:

> put another way - you want the program to ALWAYS read from EITHER a file or
> stdin and you ALWAYS want to interactively (eg. from a tty) run commands after
> reading the file - so why not just say that in the code?
> 
> # 
> #  program which does the above
> # 
> jib:~ > cat a.rb
> require 'readline'
> include Readline
> 
> inpath = ARGV.shift
> infile = inpath ? open(inpath) : STDIN
> 
> # count lines in stdin (the mail message):
> n=0; while infile.gets: n+=1 end
> puts "#{n} lines"
> 
> # always get commands interactively
> STDIN.reopen '/dev/tty' unless STDIN.tty?
> readline("type return to quit: ")
> puts "quitting..."
> 
> you could take other approaches with dup'ing and forking but this might work
> for you.

This did it!!
The essential line is: STDIN.reopen '/dev/tty' unless STDIN.tty?
and I would say that this should actually be done in Readline at the first 
call of readline. 
I rewrote my Perl program showlines:

#!/usr/bin/env ruby

#
# showlines - read lines from stdin (either file or pipe),
#             then let user interrogate lines by number

require 'readline'
include Readline

# store and count lines in stdin:
x = []
while gets: x.push($_) end
puts "#{x.size} lines"

# always get commands interactively
STDIN.reopen '/dev/tty' unless STDIN.tty?
loop do
   line = readline("type line number (0 to stop): ",true)
   if line !~ /^\d+$/
      puts "Please enter a positive integer."
   else
      number = line.to_i
      case number
      when 0
         puts "quitting..."
         exit 0
      when 1..x.size
         puts "Line #{number}:  #{x[number - 1]}"
      else
         puts "No such line."
      end
   end
end

and this now works as expected:

$ showlines <showlines
33 lines
type line number (0 to stop): 1
Line 1:  #!/usr/bin/env ruby
type line number (0 to stop): 16
Line 16:  STDIN.reopen '/dev/tty' unless STDIN.tty?
type line number (0 to stop): 33
Line 33:  end
type line number (0 to stop): 133
No such line.
type line number (0 to stop): 0
quitting...
$

Thank you very much!

-- 
Wybo