CU(1C) INTERACTIVE UNIX System CU(1C)
NAME
cu - call another UNIX system
SYNOPSIS
cu [-sspeed] [-lline] [-h] [-t] [-d] [-o | -e] [-n] telno
cu [ -s speed ] [ -h ] [ -d ] [ -o | -e ] -l line
cu [-h] [-d] [-o | -e] systemname
DESCRIPTION
The cu command calls up another UNIX system, a terminal, or
possibly a non-UNIX system. It manages an interactive
conversation with possible transfers of ASCII files.
The cu command accepts the following options and arguments:
-sspeed Specifies the transmission speed (300, 1200,
2400, 4800, 9600); The default value is "Any"
speed which will depend on the order of the
lines in the /usr/lib/uucp/Devices file. Most
modems are either 300 or 1200 baud. Directly
connected lines may be set to a speed higher
than 1200 baud.
-lline Specifies a device name to use as the communica-
tion line. This can be used to override the
search that would otherwise take place for the
first available line having the right speed.
When the -l option is used without the -s
option, the speed of a line is taken from the
Devices file. When the -l and -s options are
both used together, cu will search the Devices
file to check if the requested speed for the
requested line is available. If so, the connec-
tion will be made at the requested speed; other-
wise an error message will be printed and the
call will not be made. The specified device is
generally a directly connected asynchronous line
(e.g., /dev/ttyab) in which case a telephone
number (telno) is not required. The specified
device need not be in the /dev directory. If
the specified device is associated with an auto
dialer, a telephone number must be provided. Use
of this option with systemname rather than telno
will not give the desired result (see systemname
below).
-h Emulates local echo, supporting calls to other
computer systems which expect terminals to be
set to half-duplex mode.
-t Used to dial an ASCII terminal which has been
set to auto answer. Appropriate mapping of
carriage-return to carriage-return-line-feed
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pairs is set.
-d Causes diagnostic traces to be printed.
-o Designates that odd parity is to be generated
for data sent to the remote system.
-e Designates that even parity is to be generated
for data sent to the remote system.
-n For added security, will prompt the user to pro-
vide the telephone number to be dialed rather
than taking it from the command line.
telno When using an automatic dialer, the argument is
the telephone number with equal signs for secon-
dary dial tone or minus signs placed appropri-
ately for delays of 4 seconds.
systemname A uucp system name may be used rather than a
telephone number; in this case, cu will obtain
an appropriate direct line or telephone number
from /usr/lib/uucp/Systems. Note: the system-
name option should not be used in conjunction
with the -l and -s options as cu will connect to
the first available line for the system name
specified, ignoring the requested line and
speed.
After making the connection, cu runs as two processes: the
transmit process reads data from the standard input and,
except for lines beginning with ~, passes it to the remote
system; the receive process accepts data from the remote
system and, except for lines beginning with ~, passes it to
the standard output. Normally, an automatic DC3/DC1 proto-
col is used to control input from the remote system so the
buffer is not overrun. Lines beginning with ~ have special
meanings.
The transmit process interprets the following user-initiated
commands:
~. terminate the conversation.
~! escape to an interactive shell on the
local system.
~!cmd... run cmd on the local system (via sh -c).
~$cmd... run cmd locally and send its output to
the remote system.
~%cd change the directory on the local
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system. Note: ~!cd will cause the com-
mand to be run by a sub-shell, probably
not what was intended.
~%take from [ to ] copy file from (on the remote system) to
file to on the local system. If to is
omitted, the from argument is used in
both places.
~%put from [ to ] copy file from (on local system) to file
to on remote system. If to is omitted,
the from argument is used in both
places.
For both ~%take and put commands, as
each block of the file is transferred,
consecutive single digits are printed to
the terminal.
~~ line send the line ~ line to the remote sys-
tem.
~%break transmit a BREAK to the remote system
(which can also be specified as ~%b).
~%debug toggles the -d debugging option on or
off (which can also be specified as
~%d).
~t prints the values of the termio struc-
ture variables for the user's terminal
(useful for debugging).
~l prints the values of the termio struc-
ture variables for the remote communica-
tion line (useful for debugging).
~%nostop toggles between DC3/DC1 input control
protocol and no input control. This is
useful in case the remote system is one
which does not respond properly to the
DC3 and DC1 characters.
The receive process normally copies data from the remote
system to its standard output. Internally the program
accomplishes this by initiating an output diversion to a
file when a line from the remote begins with ~.
Data from the remote is diverted (or appended, if >> is
used) to file on the local system. The trailing ~> marks
the end of the diversion.
The use of ~%put requires stty(1) and cat(1) on the remote
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side. It also requires that the current erase and kill
characters on the remote system be identical to the current
control characters on the local system. Backslashes are
inserted at appropriate places.
The use of ~%take requires the existence of echo(1) and
cat(1) on the remote system. Also, tabs mode [see stty(1)]
should be set on the remote system if tabs are to be copied
without expansion to spaces.
When cu is used on system X to connect to system Y and sub-
sequently used on system Y to connect to system Z, commands
on system Y can be executed by using ~~. Executing a tilde
command reminds the user of the local system uname. For
example, uname can be executed on Z, X, and Y as follows:
uname
Z
~[X]!uname
X
~~[Y]!uname
Y
In general, ~ causes the command to be executed on the ori-
ginal machine, ~~ causes the command to be executed on the
next machine in the chain.
EXAMPLES
To dial a system whose telephone number is 9 201 555 1212
using 1200 baud (where dialtone is expected after the 9):
cu -s1200 9=12015551212
If the speed is not specified, "Any" is the default value.
To log in to a system connected by a direct line, enter:
cu -l /dev/ttyXX
or
cu -l ttyXX
To dial a system with the specific line and a specific
speed, enter:
cu -s1200 -l ttyXX
To dial a system using a specific line associated with an
auto dialer, enter:
cu -l culXX 9=12015551212
To use a system name, enter:
cu systemname
FILES
/usr/lib/uucp/Systems
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/usr/lib/uucp/Devices
/usr/spool/locks/LCK..(tty-device)
SEE ALSO
cat(1), ct(1C), echo(1), stty(1), uucp(1C), uname(1).
DIAGNOSTICS
Exit code is zero for normal exit, otherwise, one.
WARNINGS
The cu command does not do any integrity checking on data it
transfers. Data fields with special cu characters may not
be transmitted properly. Depending on the interconnection
hardware, it may be necessary to use a ~. to terminate the
conversion even if stty 0 has been used. Non-printing char-
acters are not dependably transmitted using either the ~%put
or ~%take commands. cu between some modems will not return
a login prompt immediately upon connection. A carriage
return will return the prompt.
BUGS
There is an artificial slowing of transmission by cu during
the ~%put operation so that loss of data is unlikely.
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