From: Dave Thomas <Dave@...>
Date: 2002-05-14T00:45:43+09:00
Subject: Re: Inline editing (non-command line)

"Berger, Daniel" <djberge@qwest.com> writes:

> I'm looking for a way to modify a file inline without using a temp file.  I
> want to do this within code, not on the command line (and no, I'm not
> interested in 'system' calls either).

I don't believe there's a way to do this on most conventional file
systems without sing some temporary storage, either memory f a
file. The reason is simple: here's a file on disk:

    |This is line one\nthis is line two\nand line three|

(On DOS the line endings are different, but the principle is the
same).

So, say you want to change all 't's to 'ZYX's. There's no room in the
current file to do it: the first time you change a 't' you'll
overwrite the next two characters as well.

There are other issues with editing in place: if it blows up half way
through, you're left with a half-changed file.

So, the conventional way to do this is to copy the original to a new
file, then when you're done rename the new file to have the same name
as the original. That's what the '-i' option to Ruby does. For example

   ruby -i -pe 'gsub(/t/, "zyx")' fred

replaces all the 't's in the file 'fred' with 'zyx'

Regards


Dave