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From: ac4@pucc-j (Tom Putnam)
Newsgroups: net.info-terms
Subject: Re: terminal emulators and invalid ESC sequence
Message-ID: <690@pucc-j>
Date: Fri, 3-Jan-86 15:32:48 EST
Article-I.D.: pucc-j.690
Posted: Fri Jan  3 15:32:48 1986
Date-Received: Sat, 4-Jan-86 05:49:02 EST
References: <171@uscvax.UUCP>
Reply-To: ac4@pucc-j.UUCP (Tom Putnam)
Distribution: net
Organization: Purdue University Computing Center
Lines: 35

In article <171@uscvax.UUCP> nadji@uscvax.UUCP (Behzad Nadji) writes:
>What is a terminal emulator supposed to do when it receives an 
>invalid escape sequence? 

I wrote a terminal emulator and had to deal with this question.  I think
there are two answers:

  1) Ignore the sequence.  The "typical" user doesn't care unless it is a
     sequence that invokes a function that he needs.  If you don't support
     that function for some reason (incomplete emulation), then your user
     isn't going to be any happier if you tell him about it.

  2) Provide a debug mode where you ignore the sequence but tell the user
     about it.  My terminal emulator uses the 25th line of the display to
     flash such messages for about 3 seconds.  I have found it is quite
     useful in debugging not only my emulator but also debugging the
     various terminal packages and systems I use it with.  I use the 25th
     line as a temporary status line (window?).  You can save it and restore
     it if necessary to provide complete emulation capabilities.  Be sure to
     include the full text of the escape sequence in the message - easy
     enough to do since you don't have to deal with non-printing control
     characters.
-- 
Tom Putnam, Manager of User Services
Purdue University Computing Center

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