Be Careful with vi -r Recovered Buffers (Unix Power Tools, 3rd Edition)

17.20. Be Careful with vi -r Recovered Buffers

Usually, when you're editing a file with vi, if you type the command ZZ, it saves your file. But if you recover a file with vi -r (Section 17.19), typing ZZ may not save your edits!

That might be a good thing. When you recover a buffer, you need to decide whether the recovered buffer is really what you want. Maybe you've made other changes to the file since then. Maybe something went wrong as the buffer was being saved (say, the system crashed). You shouldn't just save without checking first.

You can use the :w! command to write the recovered version after you're sure that you want it. Use the :q! command if you don't want the recovered version.

Another good choice is to write the recovered buffer using a different filename, then compare the recovered buffer to the original file. For example, here I recover a draft MH email message and immediately write it to a file named recovered-9 in my tmp directory. Then I use a shell escape (Section 17.21) to run diff (Section 11.1) and compare the draft file on disk (/home/jerry/Mail/drafts/9) with the copy of the recovered buffer that I just wrote (/home/jerry/tmp/recovered-9); the vi current filename % and alternate filename # shortcuts (Section 17.3) are handy here. Oops: diff shows that the recovered version has replaced the last three lines of the message on disk, in the recovered version, with more than 2,000 lines of junk!

less Section 12.3

% vi -r /home/jerry/Mail/drafts/9
    ...recovered file appears...
:w ~/tmp/recovered-9
/home/jerry/tmp/recovered-9: 55 lines, 168767 characters.
:!diff % # | less
!diff /home/jerry/Mail/drafts/9 /home/jerry/tmp/recovered-9 | less
5c5
< Subject: Re: Two more Unix Power Tools questions
---
> Subject: Next UPT (was: Re: Two more Unix Power Tools questions)
146,148c146,2182
< Yes, you mentioned it once.  Thanks for pointing that out, Greg.
< I think the next job is to review all the articles in that chapter
< to be sure which items should be included -- just the articles, or
---
> Yes, you^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
> ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
> ^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@^@
    ...zillions of lines of junk...

At this point, the best thing to do is to quit vi immediately (with :q!). Then fix up the original file by copying and pasting the good text from the copy of the recovered buffer that I just wrote. (You might want to rerun diff, outside of vi, to remind yourself which parts of the recovered file you want to transfer to the original file.) Starting a new vi session with the filenames of both the original file and the (mostly trashed) recovered buffer, as Section 17.4 explains, can make the recovery job easier.

-- JP