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Chat scripts are used in several different places, such as dialing
out on modems or logging in to remote systems. Chat scripts are made
up of pairs of strings. The program waits until it sees the first
string, known as the "expect" string, and then sends out the second
string, the "send" string.
Each chat script is defined using a set of commands. These commands
always end in a string beginning with `chat', but may start with
different strings. For example, in the `sys' file there is one set of
commands beginning with `chat' and another set beginning with
`called-chat'. The prefixes are only used to disambiguate different
types of chat scripts, and this section ignores the prefixes when
describing the commands.
Specify a chat script. The arguments to the `chat' command are
pairs of strings separated by whitespace. The first string of
each pair is an expect string, the second is a send string. The
program will wait for the expect string to appear; when it does,
the program will send the send string. If the expect string does
not appear within a certain number of seconds (as set by the
`chat-timeout' command), the chat script fails and, typically, the
call is aborted. If the final expect string is seen (and the
optional final send string has been sent), the chat script is
An expect string may contain additional subsend and subexpect
strings, separated by hyphens. If the expect string is not seen,
the subsend string is sent and the chat script continues by
waiting for the subexpect string. This means that a hyphen may
not appear in an expect string; on an ASCII system, use `\055'
An expect string may simply be `""', meaning to skip the expect
phase. Otherwise, the following escape characters may appear in
a backspace character
a newline or line feed character
a null character (for HDB compatibility)
a carriage return character
a space character
a tab character
a backslash character
character DDD, where DDD are up to three octal digits
character DDD, where DDD are hexadecimal digits.
As in C, there may be up to three octal digits following a
backslash, but the hexadecimal escape sequence continues as far as
possible. To follow a hexadecimal escape sequence with a hex
digit, interpose a send string of `""'.
A chat script expect string may also specify a timeout. This is
done by using the escape sequence `\WSECONDS'. This escape
sequence may only appear at the very end of the expect string. It
temporarily overrides the timeout set by `chat-timeout' (described
below) only for the expect string to which it is attached.
A send string may simply be `""' to skip the send phase.
Otherwise, all of the escape characters legal for expect strings
may be used, and the following escape characters are also
send an end of transmission character (`^D')
send a break character (may not work on all systems)
suppress trailing carriage return at end of send string
delay sending for 1 or 2 seconds
disable echo checking
enable echo checking
same as `BREAK' (for HDB compatibility)
pause sending for a fraction of a second
Some specific types of chat scripts also define additional escape
sequences that may appear in the send string. For example, the
login chat script defines `\L' and `\P' to send the login name and
A carriage return will be sent at the end of each send string,
unless the `\c' escape sequence appears in the string. Note that
some UUCP packages use `\b' for break, but here it means backspace.
Echo checking means that after writing each character the program
will wait until the character is echoed. Echo checking must be
turned on separately for each send string for which it is desired;
it will be turned on for characters following `\E' and turned off
for characters following `\e'.
The number of seconds to wait for an expect string in the chat
script, before timing out and sending the next subsend, or failing
the chat script entirely. The default value is 10 for a login
chat or 60 for any other type of chat.
If the STRING is seen at any time during a chat script, the chat
script is aborted. The string may not contain any whitespace
characters: escape sequences must be used for them. Multiple
`chat-fail' commands may appear in a single chat script. The
default is to have none.
This permits a chat script to be quickly aborted if an error
string is seen. For example, a script used to dial out on a modem
might use the command `chat-fail BUSY' to stop the chat script
immediately if the string `BUSY' was seen.
The `chat-fail' strings are considered in the order they are
listed, so if one string is a suffix of another the longer one
should be listed first. This affects the error message which will
be logged. Of course, if one string is contained within another,
but is not a suffix, the smaller string will always be found
before the larger string could match.
If the argument is true, all incoming characters are stripped to
seven bits when being compared to the expect string. Otherwise
all eight bits are used in the comparison. The default is true,
because some Unix systems generate parity bits during the login
prompt which must be ignored while running a chat script. This
has no effect on any `chat-program', which must ignore parity by
itself if necessary.
Specify a program to run before executing the chat script. This
program could run its own version of a chat script, or it could do
whatever it wants. If both `chat-program' and `chat' are
specified, the program is executed first followed by the chat
The first argument to the `chat-program' command is the program
name to run. The remaining arguments are passed to the program.
The following escape sequences are recognized in the arguments:
port device name
Some specific uses of `chat-program' define additional escape
Arguments other than escape sequences are passed exactly as they
appear in the configuration file, except that sequences of
whitespace are compressed to a single space character (this
exception may be removed in the future).
If the `chat-program' command is not used, no program is run.
On Unix, the standard input and standard output of the program
will be attached to the port in use. Anything the program writes
to standard error will be written to the UUCP log file. No other
file descriptors will be open. If the program does not exit with
a status of 0, it will be assumed to have failed. This means that
the dialing programs used by some versions of HDB may not be used
directly, but you may be able to run them via the `dialHDB'
program in the `contrib' directory.
The program will be run as the `uucp' user, and the environment
will be that of the process that started `uucico', so care must be
taken to maintain security.
No search path is used to find the program; a full file name must
be given. If the program is an executable shell script, it will
be passed to `/bin/sh' even on systems which are unable to execute
Here is a simple example of a chat script that might be used to
reset a Hayes compatible modem.
chat "" ATZ OK-ATZ-OK
The first expect string is `""', so it is ignored. The chat script
then sends `ATZ'. If the modem responds with `OK', the chat script
finishes. If 60 seconds (the default timeout) pass before seeing `OK',
the chat script sends another `ATZ'. If it then sees `OK', the chat
script succeeds. Otherwise, the chat script fails.
For a more complex chat script example, see See Logging In.