2.12 Automatic Setups for Different Terminals

If you work at several kinds of terminals, terminal setup can be tough. For instance, my X terminal sends a backspace character when I push the upper-right key, but the same key on another terminal sends a delete character-I want stty erase (5.9 ) to set the right erase character automatically. Maybe you want a full set of calendar programs started when you log in to the terminal at your desk, but not when you make a quickie login (2.5 ) from somewhere else.

Here are some ideas for changing your login sequence automatically. Some examples are for the C shell and use that shell's switch (47.6 ) and if (47.3 ) . Examples for Bourne-type shells use case (44.5 ) and if (44.8 ) . If you use the other type of shell, the idea still applies; just switch the syntax.

• If all you want to do is initialize your terminal (set the TERM variable (5.10 ) , set your erase character, etc.), the tset (5.3 ) command may be all you need.

• If your TERM environment variable is set differently on each terminal, you can add a test like this to your .login file:

  switch ($TERM)
  case vt100:
     ...do commands for vt100
  
     breaksw
  case xxx
  
  :
     ...do commands for xxx
  
     breaksw
  default:
     ...do commands for other terminals
  
     breaksw
  endsw

  and so on.

• If you log in from other hosts (1.33 ) or from hosts running the X window system (1.31 ) , the who am i command will probably show a hostname and/or window information in parentheses:

  bash$ who am i
  
  
  jpeek    pts/6        Jul 17 10:30   (www.jpeek.com:0.0)

  (Long hostnames may be truncated. Check yours before you write this test.) If the information in parentheses will help, add commands like these to your .profile file:

  case \(..\) \1	case "`who am i | sed -n 's/.*(\(.*\))/\1/p'`" in *0.0) ...do commands for X display 0 ;; mac2*) ...do commands for the host mac2.foo.com ;; "") ...no output (probably not a remote login) ;; *) ...do commands for other situations ;; esac

  That uses sed (34.24 ) to give the text between the parentheses for that remote host to the case . This *0.0 case matches lines ending with 0.0 , the mac2 case matches lines that start with mac2 , an empty string means sed probably didn't find any parentheses, and the * case catches everything else.

• If you know that certain port numbers are used for certain kinds of logins, you can test that. For example, many systems use ttyp0 , ttyq1 , etc. as network ports for rlogin and telnet (1.33 ) . This test will branch on the port name:

  case "`tty`" in
  /dev/tty[pqrs]?)
     # rlogin, telnet:
     ...
  /dev/tty02)
     # terminal on my desk:
     ...
  "not a tty") ;;  ...not a terminal login session; do nothing
  
  esac

• Certain systems set certain environment variables. For example, the X Window System sets a DISPLAY environment variable. (If you aren't sure about your system, use the env or printenv command (6.1 ) to look for changes in your environment at different systems.) You can test that:

  if $?	if ($?DISPLAY) then # on X window system ... else if ($?WIN_PARENT) then # on SunView system ... else ... endif

• Your system may have a /etc/ttytab or /etc/ttys file that lists the type of each terminal port. Lines in the file look something like this:

  console "/usr/etc/getty std.9600"    vt100      on  local 
  tty00   "/usr/etc/getty std.9600"    dialup     off local
  tty01   "/usr/etc/getty std.9600"    plugboard  off local
     ...
  ttyp0   none                         network    off
     ...

  (For example, port ttyp0 is network , the type used by xterm (1.31 ) , telnet (1.33 ) , and so on.)

  You can match the output of the tty (3.8 ) command, which shows your current tty, to the first column of that file. The output of tty starts with /dev or /dev/pts . So, to match your current tty to the file, you need to strip the name to its tail. For example, in bash and ksh , these three lines would put the terminal port type (vt100 , plugboard , etc.) into the ttykind shell variable:

  ${..#..} awk	tty=`tty` ttytail=${tty#/dev/} ttykind=`awk '$1 == "'$ttytail'" {print $3}' /etc/ttys`

• You can also deal with many of these cases using the venerable but obscure tset (5.3 ) program to select and initialize the correct terminal type. Another program you can use to set the terminal type is qterm (5.5 ) , available on the CD-ROM.