Re: Insert the content of a file (with command r?)

On Tue, 24 Jul 2012 13:23:41 -0500, Tim Chase <[email protected]> wrote:

> On 07/24/12 05:05, Laurent Le Brun wrote:
> > I'd like to insert the content of a file when the input matches some
> > regexp. It tried this simple script: /regexp/r file.txt
> > It works fine, except that it's inserting the content of the file
> > after the line matching the regexp. I'd like to insert it BEFORE
> > instead.
> 
> I played around with this and am not sure whether I've found an odd
> bug in GNU sed (4.2.1 on Debian stable).  I tried holding the match,
> reading the file, then printing out the held match, and it seems to
> do all the reading at the end of a cycle:
> 
>   ============insert.sed==============
>   /regexp/{
>   h       # hold the existing pattern
>   s/.*//  # delete the existing match
>   # read in the file
>   r file.txt
>   g       # return the text we held
>   }
>   ====================================
> 
> I used "4" for my regex and piped the output of "seq 10" into it to
> insert the file.txt before the "4" line. The "4" still comes out
> before the contents of file.txt does.

The command "r" just schedules the file for reading at the end of the
cycle. Here's the standard:

"The a and r commands schedule text for later output. The text specified
for the a command, and the contents of the file specified for the r
command, shall be written to standard output just before the next attempt
to fetch a line of input when executing the N or n commands, or when
reaching the end of the script. If written when reaching the end of the
script, and the -n option was not specified, the text shall be written
after copying the pattern space to standard output. The contents of the
file specified for the r command shall be as of the time the output is
written, not the time the r command is applied. The text shall be output in
the order in which the a and r commands were applied to the input."

As for the OP's problem, this should work, assuming the pattern never
occurs on the very last line of the file:

/pattern/ {
  r file.txt
  N
}

Given the way "r" works, I'm not sure there's even a way to insert the file
before the last line of the file with sed only. In that case, one can
perhaps use dirty shell tricks, like eg

{ cat input.txt; echo; } | sed program.sed | head -n -1




-- 
D.