Re: [bug-gawk] in-place edit request

[Andrew J. Schorr]

On Mon, Dec 31, 2012 at 10:18:32PM +0200, Aharon Robbins wrote:
> Now someone in the community, who thinks this feature is worthwhile,
> needs to step up to the plate and do the work.

I just whipped up a proof of concept.  It is attached.  It seems to work
on linux.  For example, these commands do the right thing:

  bash$ gawk -i inplace '{sub(/foo/, "bar"); print}' /tmp/tfile

  bash$ gawk -i inplace -v "INPLACE_SUFFIX=.bak" '{sub(/foo/, "bar"); print}' 
/tmp/tfile

It has the following known problems:

1. It uses a single static state structure, so it is not reentrant: it will
fail if BEGINFILE is called again without an intervening call to ENDFILE.
I imagine that using the fork extension could trigger a problem with this.
I'm not sure if there are any other problem scenarios.

2. It should probably register an awk_atexit handler to remove the temporary
file if gawk exits before calling ENDFILE.

3. I don't know how portable it is.  It uses the following library calls:
   stat
   mkstemp
   fchown
   fchmod
   close
   dup
   dup2
   unlink
   link
   rename

Thoughts?

Also, I'm not interested in writing a good wrapper script for this that
supports an optional backup suffix.  Somebody who really cares should 
take a crack at that.

Regards,
Andy

inplace.c
Description: Text document

inplace.awk
Description: Text document