From: "Basile Starynkevitch [news]" <basile-news@...>
Date: 2005-05-19T06:25:13+09:00
Subject: Re: (newbie Q) opposite of inspect for strings

On 2005-05-18, Thomas Adam <thomas@edulinux.homeunix.org> wrote:

(citing me, Basile S.)

>> What is is opposite of inspect for strings, ie the function parsing
>> strings external representation (as strings)?
>>
>> i.e. I do know that "a\tb".inspect gives the 6 character string
>> "\"a\\tb\"" but what is the method or function that, given the
>> argument "\"a\\tb\"" produces the "a\tb" string of 3 characters?
>
> I'll try this, assuming I understand you correctly.

Sorry for having expressed myself poorly. I mean

  a="a\tb"

binds variable a to a 3 character string (a, tab, b)

  aa=a.inspect

binds variable aa to a 6 character string (dblquote, a, backslash, t,
b, dblquote)


I'm desperately seeking a function f such that 

    b = f(aa)

binds variable b to a 3 character string which is equal to the value
of a, or I am seeking a method m such that

    c = aa.m

binds variable c to a 3 character string (a, tab, b) equal to the
value of a.


The to_s method is not a valuable substitute for m since aa.to_s is a
6 character string (equal to aa)

>
>> Also how can I easily parse (ie read) from a file such a string like
>> the output of inspect?
>

Actually I'm just trying to code in a quick and dirty way a ruby
script dumping into a textual form a (rather small) GDBM file, whoses
keys are all alphanumeric (and data are arbitrary binary strings). So
far, I've managed to code the following script which seems to work.

  #! /usr/bin/ruby
  # $Id: gdbmdump 1 2005-05-18 20:45:15Z basile $
  ## -*- ruby -*-

  require 'gdbm'

  srcdbmname=ARGV[0]
  destxtname=ARGV[1]

  STDERR.printf("start dumping gdbm %s into %s\n", srcdbmname, destxtname)

  if (not File.exists?(srcdbmname)) then
    STDERR.printf("source dbm %s does not exist\n", srcdbmname);
    exit(1)
  end

  keyarr=Array::new

  GDBM.open(srcdbmname, 0400) do |gdbm|
    nbk=0
    gdbm.each do |key,val|
      if /^[a-zA-Z0-9+*._@,!(){}-]*$/ =~ key then
        keyarr << key
        nbk = nbk + 1
      else
        STDERR.printf("bad key %s in file %s\n", key.inspect, srcdbmname);
        exit(1)
      end
    end
    STDERR.printf("got and sorting %d keys\n", nbk)
    keyarr.sort!
    if (File.exists?(destxtname)) then
      File.rename(destxtname,destxtname+"~")
    end
    File.open(destxtname, "w") do |out|
      keyarr.each do |key|
        val=gdbm[key]
        out.printf("%s\t%s\n", key, val.inspect)
      end
    end
  end

  STDERR.printf("end dumping gdbm %s into %s\n", srcdbmname, destxtname)

  ##eof $Id: gdbmdump 1 2005-05-18 20:45:15Z basile $

A typical output of the above script is

  ab      "12"
  cd      "45"

where the file starts at the column a, and where keys and data are
separated by a tabulation.

My goal was to code the corresponding loading script gdbmload; the
overall motivation for these 2 scripts is to manage under version
control (Subversion) a GDBM file (by dumping it to & reloading it from
a textual format, and by having a "canonical" dump format of it by
sorting the keys; I don"t want to version control the GDBM binary file
-because it is machine dependent- but a dump format of it, obtained
thru this gdbmdump script and the opposite gdbmload script to be
written)

I am really confused and ashamed of asking such basic questions. My
apologies to all, and a big thanks to Thomas Adam for having taken the
time to answer them.

Regards.
-- 
Basile STARYNKEVITCH         http://starynkevitch.net/Basile/ 
email: basile<at>starynkevitch<dot>net 
aliases: basile<at>tunes<dot>org = bstarynk<at>nerim<dot>net
8, rue de la Fa�encerie, 92340 Bourg La Reine, France