Watchguard Firebox X1000 Reference Manual page 107

Reference Guide
"" or ' '
Expect or send a null string. If you send a null string, it will still
send the return character. This sequence can either be a pair of
apostrophes or quotes.
\b
Backspace.
\c
Suppress the new line at the end of the reply string. This is the
only method to send a string without a trailing return character. It
must be at the end of the send string. For example, the sequence
hello\c will simply send the characters h, e, l, l, o (not valid in
expect).
\d
Delay for 1 second (not valid in expect).
\K
Insert a BREAK (not valid in expect).
\n
Send a newline or linefeed character.
\N
Send a null character. The same sequence can be represented by
\0 (not valid in expect).
\p
Pause for a fraction of a second. The delay is 1/10th of a second
(not valid in expect).
\q
Suppress writing the string to the logging system. The string
?????? is written to the log in its place (not valid in expect).
\r
Send or expect a carriage return.
\s
A space character in the string. This can be used when it is not
desirable to quote the strings that contain spaces. For example, the
sequence 'HI TIM' and HI\sTIM are the same.
Modem Initialization Strings
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