Re: What's your favourite *under_publicized* editing feature of Emacs?

[Tim X]

Giorgos Keramidas <keramida@ceid.upatras.gr> writes:

> On Sat, 29 Jan 2011 09:02:14 -0600, Perry Smith <pedzsan@gmail.com> wrote:
>> This thread is beginning to drift a bit... but something I wish I had
>> was a way to view a file without loading all of it.  I look at hugh
>> trace files and I have to get out of emacs and start a shell so I can
>> use more / less.
>>
>> The shame of it all! ;-)
>>
>> I don't know of such a critter.  If there is one, that would be super
>> cool.
>
> If there was some way to lazy-load files, I'd be happy too.
>

Many years ago I needed to load large trace files from Oracle. I just
looked and seem to have lost the code I used, but you may find the
approach useful. This was done on a Linux box and uses standard Linux
utilities. 

The basic approach I used was to write some elisp functions that created
a temporary directory, applied the 'split' program to the input file,
split the input file into manageable chunks (split will/can add a
prefix/suffix to sequence/number the chunks) and put them into the temp
directory and then open the first chunk in a buffer. I could then run
dired, which would list al the chunks and open any one of those chunks
for viewing further chunks of the file. 

I also used a defadvice around view-file which automated the process if
the file suffix was .trc. I always planned to clean it up and add a few
extra features (such as not splitting the file if it had already been
split before etc), but then my job changed a bit and I no longer had the
need to view such large trace files.

It worked quite well. Maybe not as clean as jus having a 'lazy file
read', but did mean I could view these large files from within emacs and
setting things up was largely automated. I do vaguely remember having to
play with split a bit before I got things just right. Later I added a
command that would use sed to replace strings in really large files,
which was useful when migrating large oracle databases and you wanted to
modify the paths in order to refresh a dev version with data form a
production system. Again, can't find that code as we now do things
differently and I've not kept it.

Tim


-- 
tcross (at) rapttech dot com dot au