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From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.unix.questions,comp.bugs.sys5
Subject: vi `ei:' (`modeline')
Keywords: vi passwd lookout
Message-ID: <13905@mimsy.UUCP>
Date: 8 Oct 88 00:03:33 GMT
References: <3394@dunkshot.mips.COM> <1235@cbnews.ATT.COM> <13215@hqda-ai.ARPA>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 25

In article <13215@hqda-ai.ARPA> jay@hqda-ai.ARPA (Jay Hiser) writes:
>... but SysV vi has an interesting bug/feature that can cause a problem.
>
>CCI, our SysV vender, has just posted a bulletin warning that vi has
>an undocumented feature.  "[it was] designed to look for the
>occurrence of a line that starts with the string "ei:" and use the
>characters following the ei: as editor commands.  This is NOT
>documented."

This bulletin is correct in point of fact but is wrong in spirit.
What really happens is that vi is looking for `mode lines' consisting
of `ex:<commands>' or `vi:<commands>'.  Such lines must appear within
the first or last 5 (10?) lines of the file being edited.

Now, the code that checks for `mode lines' is rather sloppy.  Not only
does it match on `ex' and `vi', it also matches on `ei' and `vx'.  And
in 4.2BSD (and perhaps some SysV releases---no telling which ones since
the release numbering is so bizarre) you cannot turn it off!  More modern
vi's have a `modeline' option, so that you must `set modeline' before
editing such a file if you want mode line commands to take effect.
`set nomodeline' in your .exrc or $EXINIT or ./.exrc and the editor
will ignore mode line commands.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris