Linux Network Administrator Guide, Second Edition

A dip Reference

In this section, we will give a reference for most of dip 's commands. You can get an overview of all the commands it provides by invoking dip in test mode and entering the help command. To learn about the syntax of a command, you may enter it without any arguments. Remember that this does not work with commands that take no arguments. The following example illustrates the help command:

# dip -t
DIP: Dialup IP Protocol Driver version 3.3.7p-uri (25 Dec 96)
Written by Fred N. van Kempen, MicroWalt Corporation.
Debian version 3.3.7p-2 (debian).
DIP› help
DIP knows about the following commands:
 beep bootp break chatkey config
 databits dec default dial echo
 flush get goto help if
 inc init mode modem netmask
 onexit parity password proxyarp print
 psend port quit reset securidfixed
 securid send shell skey sleep
 speed stopbits term timeout wait
DIP› echo
Usage: echo on|off
DIP›

Throughout the following section, examples that display the DIP› prompt show how to enter a command in test mode and what output it produces. Examples lacking this prompt should be taken as script excerpts.

The modem commands

dip provides a number of commands that configure your serial line and modem. Some of these are obvious, such as port, which selects a serial port, and speed, databits, stopbits, and parity, which set the common line parameters. The modem command selects a modem type. Currently, the only type supported is HAYES (capitalization required). You have to provide dip with a modem type, or else it will refuse to execute the dial and reset commands. The reset command sends a reset string to the modem; the string used depends on the modem type selected. For Hayes-compatible modems, this string is ATZ.

The flush code can be used to flush out all responses the modem has sent so far. Otherwise, a chat script following reset might be confused because it reads the OK responses from earlier commands.

The init command selects an initialization string to be passed to the modem before dialing. The default for Hayes modems is 'ATE0 Q0 V1 X1', which turns on echoing of commands and long result codes, and selects blind dialing (no checking of dial tone). Modern modems have a good factory default configuration, so this is a little unnecessary, though it does no harm.

The dial command sends the initialization string to the modem and dials up the remote system. The default dial command for Hayes modems is ATD.

The echo command

The echo command serves as a debugging aid. Calling echo on makes dip echo to the console everything it sends to the serial device. This can be turned off again by calling echo off.

dip also allows you to leave script mode temporarily and enter terminal mode. In this mode, you can use dip just like any ordinary terminal program, writing the characters you type to the serial line, reading data from the serial line, and displaying the characters. To leave this mode, enter Ctrl-].

The get command

The get command is dip 's way of setting a variable. The simplest form is to set a variable to a constant, as we did in cowslip.dip. You may, however, also prompt the user for input by specifying the keyword ask instead of a value:

DIP› get $local ask
Enter the value for $local: _

A third method is to obtain the value from the remote host. Bizarre as it seems at first, this is very useful in some cases. Some SLIP servers will not allow you to use your own IP address on the SLIP link, but will rather assign you one from a pool of addresses whenever you dial in, printing some message that informs you about the address you have been assigned. If the message looks something like ' Your address: 192.168.5.74 ', the following piece of dip code would let you pick up the address:

# finish login
wait address: 10
get $locip remote

The print command

This is the command used to echo text to the console from which dip was started. Any of dip 's variables may be used in print commands. Here's an example:

DIP› print Using port $port at speed $speed
Using port ttyS3 at speed 38400

Variable names

dip understands only a predefined set of variables. A variable name always begins with a dollar symbol and must be written in lowercase letters.

The $local and $locip variables contain the local host's name and IP address. When you store the canonical hostname in $local, dip will