From: Dossy <dossy@...>
Date: 2003-02-06T20:45:16+09:00
Subject: Re: %L, %l revisited

On 2003.02.06, Tom Sawyer <transami@transami.net> wrote:
> 
> that is an good use of HERE docs. i did not know you could embed them in 
> methods until i ran this. that's useful. i like them more now.

You ought to read this very well-written article on here-docs, written
by Randal Schwartz:

Unix Review Column 12 (January 1997)
http://www.stonehenge.com/merlyn/UnixReview/col12.html

My personal favorite and not commonly known feature of here-docs:

irb(main):015:0> puts <<`SHELL`
irb(main):016:0`   for i in *; do
irb(main):017:0`   echo $i
irb(main):018:0`   done
irb(main):019:0` SHELL
[..my files snipped..]
nil

> for myself i think i'd still lean toward assigning variables to pass
> into the method for clearity,

Here-docs improve clarity, usually.

> > anyway.  Shell scripting languages already have it before there was
> > perl. But, I do not know if it originated from sh or something even
> > more ancient.
> 
> really, that old?

Yes, that old.

The Traditional Bourne Shell Family
http://www.uni-ulm.de/~s_smasch/bourne/

This page links to Version 7's Bourne shell manpage (supposedly from
1979) which documents here-docs (without calling them here-docs way back
when) like so:

     <<word
      The shell input is read up to a line the same as  word,
      or  end  of  file.   The resulting document becomes the
      standard input.  If any character  of  word  is  quoted
      then no interpretation is placed upon the characters of
      the document; otherwise, parameter and command  substi-
      tution  occurs,  \newline  is ignored, and \ is used to
      quote the characters \ $ ` and the first  character  of
      word.

Apparently, the improvement of "<<-word" here-docs that strip leading
tabs only came two years later, in 1981:

    o here document with trailing dash "<<-" strips leading tabs 

It seems that Ruby's here-doc doesn't implement this:

irb(main):001:0> p <<-"EOT"
irb(main):002:0"        this is
irb(main):003:0"        a test
irb(main):004:0" EOT
"\tthis is\n\ta test\n"
nil

I'm generating the tabs using ^V^I in irb ... at least Ruby parsed it as
a here-doc, even if it didn't strip the tabs ...

-- Dossy

-- 
Dossy Shiobara                       mail: dossy@panoptic.com 
Panoptic Computer Network             web: http://www.panoptic.com/ 
  "He realized the fastest way to change is to laugh at your own
    folly -- then you can let go and quickly move on." (p. 70)