wja@iclbra.UUCP (Wayne Alston) (05/23/85)
An undocumented feature in vi allows a valid command in the file being
'edited' of the form
...ex:{command}:
or
...vi:{command}:
to be actioned before interactive editing is allowed. However, the bug also
permits the variants ei and vx. The code reads:-
if (beg[-2] != 'e' && beg[-2] != 'v') return;
if (beg[-1] != 'x' && beg[-1] != 'i') return;
in routine checkmodeline().
The bug was discovered by trying to install a user with the initials 'jei' into
/etc/passwd.
Note that the above structure need not be at the beginning of the file.
Try vi'ing a file containing ei:x: .
Wayne Alston
..!reading!iclbra!wjawcs@ho95b.UUCP (Bill Stewart) (05/25/85)
Wayne Allston at ICL had some comments about the "vi-startup-mode" feature:
1) It's undocumented
2) It also accepts ei: and vx: in addition to ex: and vi:
3) It's more of a misfeature than a feature (paraphrased.)
Well, 2) is clearly a bug, and "somebody" ought to fix it. I just checked
the source for version 3.9, and the offending lines of code are still there
in checkmodeline().
However, the startup mode is not undocumented, and it's not a misfeature.
Admittedly, the documentation isn't in the manual page, it's in the file
vax/ex.news in the source directory, but this applies to any features added
since the vi 3.5 version came out. (Hope you've got source! :~)
Whether it's a good feature is somewhat of a religious argument, but I like
it. However, it would be nice to have a modelines/nomodelines option that
you could set in $EXINIT, to make it safer to edit important files, or other
files where the magic sequences might occur.
--
Bill Stewart 1-201-949-0705
AT&T Bell Labs, Room 4K-435, Holmdel NJ
{ihnp4,allegra,cbosgd,vax135}!ho95c!wcsmark@cbosgd.UUCP (Mark Horton) (05/25/85)
This problem is well known - it came out about a year ago. It has been fixed in vi 3.10. The syntax is now something that's unlikely to show up by accident in text files, and very few commands are allowed in a mode line. There are explicit checks to prevent ! commands, too. 3.10 will probably first be released in System V Release 3. Mark
guy@sun.uucp (Guy Harris) (05/25/85)
> An undocumented feature in vi allows a valid command in the file being > 'edited' of the form > > ...ex:{command}: > or > ...vi:{command}: > > to be actioned before interactive editing is allowed. However, the bug > also permits the variants ei and vx. The feature(?) and the bug are in ex/vi 3.7 as well, which comes with 4.2BSD. > The bug was discovered by trying to install a user with the initials 'jei' > into /etc/passwd. The fact that mode-line processing can't be turned off is, arguably, a bug (the same thing may have bitten us here; "vi" acted strangely when editing /etc/passwd, and I think there was an entry that looked like a mode line). Somebody posted some changes to "ex" (which apply both the 4.2BSD's 3.7 and System V Release 2's 3.9) which added a flag "modelines" which, when on, enabled mode-line processing; the default was to disable mode-line processing. Guy Harris
honey@down.FUN (Peter Honeyman) (05/28/85)
the fact that the modelines search is for the pattern [ev][xi]: rather than for (ex|vi): aggravates the problem. peter