cu takes a single argument, besides the options. If the argument is the string "dir" cu will make a direct connection to the port. This may only be used by users with write access to the port, as it permits reprogramming the modem.

Otherwise, if the argument begins with a digit, it is taken to be a phone number to call. Otherwise, it is taken to be the name of a system to call. The -z or --system option may be used to name a system beginning with a digit, and the -c or --phone option may be used to name a phone number that does not begin with a digit.

cu locates a port to use in the UUCP configuration files. If a simple system name is given, it will select a port appropriate for that system. The -p, --port, -l, --line, -s and --speed options may be used to control the port selection.

When a connection is made to the remote system, cu forks into two processes. One reads from the port and writes to the terminal, while the other reads from the terminal and writes to the port.

cu provides several commands that may be used during the conversation. The commands all begin with an escape character, initially ~ (tilde). The escape character is only recognized at the beginning of a line. To send an escape character to the remote system at the start of a line, it must be entered twice. All commands are either a single character or a word beginning with % (percent sign).

cu recognizes the following commands:

~.

Terminate the conversation.

~! command

Run command in a shell. If command is empty, starts up a shell.

~$ command

Run command, sending the standard output to the remote system.

~| command

Run command, taking the standard input from the remote system.

~+ command

Run command, taking the standard input from the remote system and sending the standard output to the remote system.

~#, ~%break

Send a break signal, if possible.

~c directory, ~%cd directory

Change the local directory.

~> file

Send a file to the remote system. This just dumps the file over the communication line. It is assumed that the remote system is expecting it.

~<

Receive a file from the remote system. This prompts for the local file name and for the remote command to execute to begin the file transfer. It continues accepting data until the contents of the eofread variable are seen.

~p from to, ~%put from to

Send a file to a remote Unix system. This runs the appropriate commands on the remote system.

~t from to, ~%take from to

Retrieve a file from a remote Unix system. This runs the appropriate commands on the remote system.

~s variable value

Set a cu variable to the given value. If value is not given, the variable is set to true.

~! variable

Set a cu variable to false.

~z

Suspend the cu session. This is only supported on some systems. On systems for which ^Z may be used to suspend a job, ~^Z will also suspend the session.

~%nostop

Turn off XON/XOFF handling.

~%stop

Turn on XON/XOFF handling.

~v

List all the variables and their values.

~?

List all commands.

cu also supports several variables. They may be listed with the ~v command, and set with the ~s or ~! commands.

escape

The escape character. Initially ~ (tilde).

delay

If this variable is true, cu will delay for a second after recognizing the escape character before printing the name of the local system. The default is true.

eol

The list of characters which are considered to finish a line. The escape character is only recognized after one of these is seen. The default is carriage return, ^U, ^C, ^O, ^D, ^S, ^Q, ^R.

binary

Whether to transfer binary data when sending a file. If this is false, then newlines in the file being sent are converted to carriage returns. The default is false.

binary-prefix

A string used before sending a binary character in a file transfer, if the binary variable is true. The default is ^V.

echo-check

Whether to check file transfers by examining what the remote system echoes back. This probably doesn't work very well. The default is false.

echonl

The character to look for after sending each line in a file. The default is carriage return.

timeout

The timeout to use, in seconds, when looking for a character, either when doing echo checking or when looking for the echonl character. The default is 30.

kill

The character to use delete a line if the echo check fails. The default is ^U.

resend

The number of times to resend a line if the echo check continues to fail. The default is 10.

eofwrite

The string to write after sending a file with the ~> command. The default is ^D.

eofread

The string to look for when receiving a file with the ~< command. The default is $, which is intended to be a typical shell prompt.

verbose

Whether to print accumulated information during a file transfer. The default is true.

-e, --parity=even

Use even parity.

-o, --parity=odd

Use odd parity.

--parity=none

Use no parity. No parity is also used if both -e and -o are given.

-h, --halfduplex

Echo characters locally (half-duplex mode).

--nostop

Turn off XON/XOFF handling (it is on by default).

-E char, --escape char

Set the escape character. Initially ~ (tilde). To eliminate the escape character, use -E ''.

-z system, --system system

The system to call.

-c phone-number, --phone phone-number

The phone number to call.

-p port, --port port

Name the port to use.

-a port

Equivalent to --port port.

-l line, --line line

Name the line to use by giving a device name. This may be used to dial out on ports that are not listed in the UUCP configuration files. Write access to the device is required.

-s speed, --speed speed

The speed (baud rate) to use.

-#

Where # is a number, equivalent to --speed #.

-n, --prompt

Prompt for the phone number to use.

-d

Enter debugging mode. Equivalent to --debug all.

-x type, --debug type

Turn on particular debugging types. The following types are recognized: abnormal, chat, handshake, uucp-proto, proto, port, config, spooldir, execute, incoming, outgoing. Only abnormal, chat, handshake, port, config, incoming and outgoing are meaningful for cu.

Multiple types may be given, separated by commas, and the --debug option may appear multiple times. A number may also be given, which will turn on that many types from the foregoing list; for example, --debug 2 is equivalent to --debug abnormal,chat. --debug all may be used to turn on all debugging options.

-I file, --config file

Set configuration file to use. This option may not be available, depending upon how cu was compiled.

-v, --version

Report version information and exit.

--help

Print a help message and exit.