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From: cottrell@NBS-VMS.ARPA (COTTRELL, JAMES)
Newsgroups: net.unix-wizards
Subject: Shell Filter
Message-ID: <2197@brl-tgr.ARPA>
Date: Wed, 16-Oct-85 15:12:59 EDT
Article-I.D.: brl-tgr.2197
Posted: Wed Oct 16 15:12:59 1985
Date-Received: Fri, 18-Oct-85 01:25:23 EDT
Sender: news@brl-tgr.ARPA
Lines: 36

/*
> >     I am trying to write a filter for the shell.  The  idea
> >is  to  trap  commands  and carry out certain actions before
> >passing a possibly modified command on to the  shell.   This
> >seemingly simple task is proving rather difficult.
> 
> Your idea for using ptty's seems sound.  I have done much the same
> using named pipes on sysV.  For the filter, I would try it using m4,
> or awk if your processing is complicated.  There are only a couple
> cases where you would have to turn off pre-processing to send raw
> data to a program, such as a hereis (<<) document or quoted strings.
> In awk, you could implement that by setting a flag when those
> structures are encountered.

Try hacking on script. We have a terminal here that xmt's upper
case when unshifted, lower case when shifted. You heard me right.
The first thing I did was flip the case on all incoming alfa's.
The damn thing also uses ^Z for backspace instead of ^H, which is
hardwired into the tty driver, so I change ^H to ^Z. But wait!
Cursor addressing is ^C, Y, X, where X & Y are unbiased! So I have
to have a state machine allowing the next two chars literally.
There's more. It seems that stty nl[1-3] cr[1-3] don't send
nulls, so I have to do my own padding. Etcetera...

There is no reason why you couldn't do history or anything else
you wanted to do here as well.

My own question: I would like to put my VT220 to work in VT220 mode
instead of running it in VT100 mode. Unfortunately it believes in
the parity bit & goes into weird character set mode. Is there any
way to force the parity bit always off under BSD4.2? If not, I'll
have to hack script again.....

	jim		cottrell@nbs
*/
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