[SOLVED] Trailing "m"s at the end of every line when viewing man pages

[Stephen Powell <zlinuxman@wowway.com>]

On Mon, 06 Apr 2015 13:46:45 -0400 (EDT), Bob Proulx wrote:
> 
> I would try dumping a man page to a file and then examining the file
> to understand if the 'm's are in the man output or an artifact of
> browsing on the terminal with less.

Here's what I did.  On a terminal other than my 3151, I issued the
following commands:

script script.output
TERM=ibm3161 man man
q
exit
reset

Now, by examining script.output, I was able to determine that each
line ends with ^[[m.  That's escape, left square bracket, m.
This appears to be an escape sequence for turning off special modes,
such as high intensity, reverse video, blink, etc.  This is an
ANSI standard escape sequence.  The problem is, this terminal does
not conform to the ANSI standard.  The correct code for this terminal
to do the above is ^[4@.  That's escape, 4, at sign.  This is clearly
a bug, probably in grotty, which just assumes that all terminals
conform to the ANSI standard.  They don't.  This terminal recognizes
the ^[[ as an invalid combination and throws it away.  The trailing m
is then displayed literally.

A related problem is that agetty does not clear the screen.  The clear
command, issued at a Linux shell prompt, works.  The clear command
consults the terminfo database to determine the proper control sequence
for the current terminal type ($TERM environment variable) to clear
the screen.  But agetty, it seems, sends the most common control
sequence used to clear the screen, which doesn't work on this terminal.

Here's how I fixed it, or rather, how I worked around it.  First of
all I use the --noclear option of agetty:

/sbin/agetty -8 --noclear ttyS0 38400 ibm3161

Instead, I clear the screen on logout, with this logic in ~/.bash_logout:

if [ "$SHLVL" = 1 ]
then
        if [ "$TERM" = "ibm3161" ]
        then
                clear
        fi
fi

I wrote a shell script, which I place in my ~/bin directory.  The
name of the script is mypager, which is marked executable, of course,
with "chmod +x mypager".  Here is what it looks like:

#!/bin/sh
sed -e 's/^[\[m$/^[4@/'|less -r

That's not a circumflex followed by a left square bracket.  That's the
escape character.  In input mode in vi, I entered it with the ^V^[ sequence,
since otherwise, it would cause vi to exit input mode.

I also have the following logic in ~/.bashrc:

if [ "$TERM" = "ibm3161" ]
then
        LANG=en_US
        LESS="-h0 -d"
        MANOPT="-P mypager -7"
        export LESS MANOPT
fi

Problem solved.  But this is a workaround.  There are two bugs.  One is in
agetty for not sending the right clear code.  The other is in grotty
(probably) for not sending the right "turn off special modes" code.

Thanks to all those who helped.

-- 
  .''`.     Stephen Powell    <zlinuxman@wowway.com>
 : :'  :
 `. `'`
   `-