ch02_12.htm

the unix power tools

>If you know that certain port numbers are used for certain kinds of
logins, you can test that.
For example, many systems use <EM
CLASS="emphasis"
>ttyp0</EM
>, <EM
CLASS="emphasis"
>ttyq1</EM
>, etc. as network
ports for<A
CLASS="indexterm"
NAME="AUTOID-3530"
></A
><A
CLASS="indexterm"
NAME="AUTOID-3532"
></A
>
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>rlogin</EM
> and <EM
CLASS="emphasis"
>telnet</EM
> (<A
CLASS="linkend"
HREF="ch01_33.htm"
TITLE="UNIX Networking and Communications "
>1.33</A
>)</SPAN
>.
This test will branch on the port name:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>case &quot;`tty`&quot; in
/dev/tty[pqrs]?)
   # rlogin, telnet:
   ...
/dev/tty02)
   # terminal on my desk:
   ...
&quot;not a tty&quot;) ;;  <I
CLASS="lineannotation"
>...not a terminal login session; do nothing</I
>
esac</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
></P
></LI
><LI
CLASS="listitem"
><P
CLASS="para"
><A
CLASS="indexterm"
NAME="AUTOID-3543"
></A
><A
CLASS="indexterm"
NAME="AUTOID-3545"
></A
><A
CLASS="indexterm"
NAME="AUTOID-3549"
></A
>Certain systems set certain environment variables.
For example, the X Window System sets a <EM
CLASS="emphasis"
>DISPLAY</EM
> environment variable.
(If you aren't sure about your system, use the
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>env</EM
> or <EM
CLASS="emphasis"
>printenv</EM
> command (<A
CLASS="linkend"
HREF="ch06_01.htm#UPT-ART-1170"
TITLE="What Environment Variables Are Good For "
>6.1</A
>)</SPAN
>
to look for changes in your environment at different systems.)
You can test that:</P
><P
CLASS="para"
><TABLE
CLASS="screen.co"
BORDER="1"
><TR
><TH
VALIGN="TOP"
><PRE
CLASS="calloutlist"
>
<A
CLASS="co"
HREF="ch47_03.htm"
TITLE="47.3 Conditional Statements with if "
>if</A
> <A
CLASS="co"
HREF="ch47_04.htm"
TITLE="47.4 C Shell Variable Operators and Expressions "
>$?</A
> 






&#13;</PRE
></TH
><TD
VALIGN="TOP"
><PRE
CLASS="screen"
>
if ($?DISPLAY) then
   # on X window system
   ...
else if ($?WIN_PARENT) then
   # on SunView system
   ...
else
   ...
endif</PRE
></TD
></TR
></TABLE
></P
><P
CLASS="para"
></P
></LI
><LI
CLASS="listitem"
><P
CLASS="para"
><A
CLASS="indexterm"
NAME="AUTOID-3562"
></A
><A
CLASS="indexterm"
NAME="AUTOID-3564"
></A
><A
CLASS="indexterm"
NAME="AUTOID-3566"
></A
><A
CLASS="indexterm"
NAME="AUTOID-3568"
></A
>Your system may have a <EM
CLASS="emphasis"
>/etc/ttytab</EM
> or
<EM
CLASS="emphasis"
>/etc/ttys</EM
> file that lists the type of each terminal port.
Lines in the file look something like this:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>console &quot;/usr/etc/getty std.9600&quot;    vt100      on  local 
tty00   &quot;/usr/etc/getty std.9600&quot;    dialup     off local
tty01   &quot;/usr/etc/getty std.9600&quot;    plugboard  off local
   ...
ttyp0   none                         network    off
   ...</PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>(For example, port <EM
CLASS="emphasis"
>ttyp0</EM
> is <EM
CLASS="emphasis"
>network</EM
>, the type used by
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>xterm</EM
> (<A
CLASS="linkend"
HREF="ch01_31.htm"
TITLE="The X Window System "
>1.31</A
>)</SPAN
>,
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>telnet</EM
> (<A
CLASS="linkend"
HREF="ch01_33.htm"
TITLE="UNIX Networking and Communications "
>1.33</A
>)</SPAN
>,
and so on.)</P
><P
CLASS="para"
>You can match the output of the
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>tty</EM
> (<A
CLASS="linkend"
HREF="ch03_08.htm"
TITLE="What tty Am I On? "
>3.8</A
>)</SPAN
>
command, which shows your current tty, to the first column of that
file.
The output of <EM
CLASS="emphasis"
>tty</EM
> starts with <EM
CLASS="emphasis"
>/dev</EM
> or <EM
CLASS="emphasis"
>/dev/pts</EM
>.
So, to match your current tty to the file, you need to strip the
name to its tail.
For example, in <EM
CLASS="emphasis"
>bash</EM
> and <EM
CLASS="emphasis"
>ksh</EM
>, these three lines would
put the terminal port type (<CODE
CLASS="literal"
>vt100</CODE
>, <CODE
CLASS="literal"
>plugboard</CODE
>, etc.)
into the <EM
CLASS="emphasis"
>ttykind</EM
> shell variable:</P
><P
CLASS="para"
><TABLE
CLASS="screen.co"
BORDER="1"
><TR
><TH
VALIGN="TOP"
><PRE
CLASS="calloutlist"
>
&#13;<A
CLASS="co"
HREF="ch09_07.htm"
TITLE="9.7 String Editing in ksh and bash "
>${..#..}</A
> 
<A
CLASS="co"
HREF="ch33_11.htm"
TITLE="33.11 Quick Reference: awk "
>awk</A
> </PRE
></TH
><TD
VALIGN="TOP"
><PRE
CLASS="screen"
>
tty=`tty`
ttytail=${tty#/dev/}
ttykind=`awk '$1 == &quot;'$ttytail'&quot; {print $3}' /etc/ttys`</PRE
></TD
></TR
></TABLE
></P
><P
CLASS="para"
></P
></LI
><LI
CLASS="listitem"
><P
CLASS="para"
>You can also deal with many of these cases using the venerable but
obscure <A
CLASS="indexterm"
NAME="AUTOID-3599"
></A
>
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>tset</EM
> (<A
CLASS="linkend"
HREF="ch05_03.htm"
TITLE="Setting the Terminal Type When You Log In "
>5.3</A
>)</SPAN
>
program to select and initialize the correct terminal type.
Another program you can use to set the terminal type is 
<SPAN
CLASS="link"
><EM
CLASS="emphasis"
>qterm</EM
> (<A
CLASS="linkend"
HREF="ch05_05.htm"
TITLE="Querying Your Terminal Type: qterm "
>5.5</A
>)</SPAN
>,
available on the CD-ROM.</P
></LI
></UL
><DIV
CLASS="sect1info"
><P
CLASS="SECT1INFO"
>- <SPAN
CLASS="authorinitials"
>JP</SPAN
></P
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