ckcbwr.txt

C-Kermit源码。是使用串口/Modem和网络通讯的程序

patient and let Kermit "drain" them.

If C-Kermit is sending a file, remote-mode packet-mode breakout (Ctrl-C Ctrl-C
by default) is not effective until after C-Kermit sends its first packet.  If
C-Kermit is receiving a file or is in server mode, it will be effective right
away.  In the former case, the SET DELAY value determines the earliest time at
which you can break out of packet mode.

Some communication programs have errors in their implementation of Kermit
attribute packets.  If you get an error message from your communication
program like "Attribute error", tell C-Kermit to SET ATTRIBUTES OFF.  Better
yet, switch to a real Kermit program, such as MS-DOS Kermit.

When using C-Kermit to transfer files with the HP48SX calculator, you must
SET FLOW NONE.  The HP48SX does not support flow control, and evidently also
becomes confused if you attempt to use it.  You might also need to use
SET SEND PAUSE 100 (or other number).

The fullscreen file transfer display will not work right if your terminal type
is set incorrectly, or is not known to the host operating system.  Even when
it does work, it might slow down your file transfers a bit, especially on
high-speed network connections.  On certain small computers, it has been
reported to cause increased disk activity due to swapping or paging.  The
fullscreen display is not particularly useful with speaking or Braille devices.
In these cases, use SET FILE DISPLAY CRT or SET FILE DISPLAY SERIAL.

If you have trouble transferring files over a TCP/IP connection, give the
command:

  SET PARITY SPACE

and try again.  If that doesn't work, also try a shorter packet length.

On the other hand, if file transfers through a TCP/IP connection work, but are
very slow, use a longer packet length, 2000 or more, and also try increasing
the window size.  Also, make sure FLOW is NONE since TCP/IP handles flow
control itself, and XON/XOFF processing only slows things down.

Some communication software claims to implement sliding windows, but does so
incorrectly.  If sliding window transfers fail, set C-Kermit's window size to
the smallest one that works, for example:

  SET WINDOW 1

The UNIX version of C-Kermit discards carriage returns when receiving files
in text mode.  Thus, "bare" carriage returns (sometimes used to achieve
overstriking) are lost.

SET FILE COLLISION BACKUP is the default.  This means:

 - If you send the same file lots of times, there will be many backup files.
   There is no automatic mechanism within Kermit to delete them, no notion of
   a "version retention count", etc, but you can use the PURGE command to
   clean them up.

 - If a file arrives that has the same name as a directory, the file transfer
   fails because Kermit will not rename a directory.  Send the file with
   another name, or use SET FILE COLLISION RENAME.

 - If the directory lacks write permission, the file transfer fails even if
   you have write access to the file that is being backed up; in that case,
   switch to SET FILE COLLISION OVERWRITE or APPEND, or send to a different
   directory.

SET FILE COLLISION UPDATE depends on the date/time stamp in the attribute
packet.  However, this is recorded in local time, not Universal Time (GMT),
and there is no indication of time zone.  The time is expressed to the
precision of 1 second, but some file systems do not record with this precision
-- for example, MS-DOS records the file date/time only to the nearest 2
seconds.  This might cause update operations to send more files than
necessary.

(This paragraph does NOT apply to UNIX, where, as of C-Kermit 6.1, C-Kermit
pipes incoming mail and print material directly the mail or print program):
When C-Kermit is receiving files from another Kermit program that has been
given the MAIL or REMOTE PRINT command, C-Kermit follows the current filename
collision action.  This can be disconcerting if the action was (for example)
BACKUP, because the existing file will be renamed, and the new file will be
mailed (or printed) and then deleted.  Kermit cannot temporarily change to
RENAME because the file collision action occurs when the filename packet is
received, and the PRINT or MAIL disposition only comes later, in the Attribute
packet.

Execution of multiple file transfers by C-Kermit from a command file when
in remote mode might exhibit long delays between each transfer.  To avoid
this, just include the command "SET DELAY 0" in your command file before any
of the file-transfer commands.


(13) SCRIPT PROGRAMMING

13.1. Comments Versus the SCRIPT Command

Remember that ";" and "#" introduce comments when (a) they are the first
character on the line, or (b) they are preceded by at least one blank or
tab within a line.  Thus constructions like:

  INPUT 5 ;
  SCRIPT ~0 #--#--#

must be coded using backslash notation to keep the data from being ignored:

  INPUT 5 \59			; 59 is the decimal ASCII code for ";"
  SCRIPT ~0 \35--#--#		; 43 is the decimal ASCII code for "#"

or, more simply:

  INPUT 5 \;                    ; Just quote the semicolon
  SCRIPT ~0 \#--#--#            ; Just quote the "#"

13.2. Alphabetic Case and the INPUT Command

INPUT and REINPUT caseless string comparisons do not work for non-ASCII
(international) characters.  Workaround: SET INPUT CASE OBSERVE.  Even then,
the "lexically less than" and "lexically greater than" operations (IF LLT, IF
LGT) probably won't work as expected.  The same is true for the
case-conversion functions \Flower() and \Fupper().  C-Kermit does not know the
collating sequence for different character sets and languages.  (On the other
hand, it might work depending on such items as how Kermit was linked, whether
your operating supports "locales", etc)

13.3. NUL (0) Characters in C-Kermit Commands

You can't include a NUL character (\0) in C-Kermit command text without
terminating the character string in which it appears.  For example:

  echo In these brackets [\0] is a NUL

will echo "In these brackets [".  This applies to ECHO, INPUT, OUTPUT, and all
other commands (but you can represent NUL by "\N" in an OUTPUT string).  This
is because C-language strings are terminated internally by the NUL character,
and it allows all of C-Kermit's string comparison and manipulation functions
to work in the normal "C" way.

To illustrate:
  INPUT 5 \0
is equivalent to:
  INPUT 5
and:
  INPUT 5 ABC\0DEF
is equivalent to:
  INPUT 5 ABC

INPUT operations discard and ignore NUL characters that arrive from the
communication device, meaning that they do not figure into matching operations
(e.g. A<NUL>B matches AB); they are not deposited in the INPUT buffer
(\v(input)); and they are not counted in \v(incount), with two exceptions:

  1. An arriving NUL character restarts the INPUT SILENCE timer.

  2. An arriving NUL character terminates the INPUT command with the
     SUCCESS condition if the INPUT command was given an empty search
     string.  In this case \v(incount) is set to 1.

Also, the \v(inchar) variable is null (completely empty) if the last INPUT
character was NUL.  That is, there is no way to tell only by looking at
\v(inchar) the difference between a NUL that was INPUT and no INPUT at all.
If the INPUT command succeeded but \v(inchar) is empty, then a NUL character
was input.  Also, \v(incount) will be set to 1.

\v(incount) and \v(inchar) are NOT affected by the CLEAR command.

13.4. \ffiles() and \fnextfile() Peculiarities

The following script program:

  for \%i 1 \ffiles(oofa.*) 1 {
      send \fnextfile()
  }

did not work as expected in C-Kermit 6.0 and earlier but does work in
C-Kermit 6.1 and later.

13.5. Commands That Have Only Local Effect

Certain settings are local to each command level, meaning that subordinate
command levels (macros or command files) can change them without affecting
their values at higher command levels.  When a new command level is invoked,
the value is inherited from the previous level.  These settings are:

  CASE
  COUNT and \v(count)
  INPUT CASE
  INPUT TIMEOUT
  MACRO ERROR
  TAKE ERROR

This arrangement allows CASE, TIMEOUT, and ERROR settings, which are used to
control automatic exit from a command file or macro upon error, to be
automatically restored when the command file or macro exits.

The COUNT variable follows this rule too, which permits nested SET COUNT /
IF COUNT loops, as in this example in which the inner loop counts down from
the current COUNT value of the outer loop (try it):

  DEFINE INNER WHILE COUNT { WRITE SCREEN {   Inner:}, SHOW COUNT }
  SET COUNT 5
  WHILE COUNT { WRITE SCREEN Outer:, SHOW COUNT, DO INNER }

Keep in mind that an inferior command level cannot manipulate the COUNT
value held by a higher level.  For example:

  DEFINE OOFA SHOW COUNT, IF COUNT GOTO LOOP
  SET COUNT 5
  :LOOP
  OOFA
  ECHO Done

results in an infinite loop; the COUNT value remains at 5 because it is never
decremented at the same level at which it was set.

NOTE: "WHILE COUNT" did not work prior to edit 095 of ckuusr.c, 19 Jan 93.

13.6. Literal Braces in Function Calls

Since braces are used in function calls to indicate grouping, there is no way
to pass literal braces to the function itself.  Solution: Define a variable
containing the string that has braces.  Example:

  define \%a ab{cd
  echo \fsubstring(\%a)
  ab{cd

If the string is to start with a leading brace and end with a closing brace,
then double braces must appear around the string (which itself is enclosed in
braces):

  define \%a {{{foo}}}
  echo \fsubstring(\%a)
  {foo}

This also works for any other kind of string:

  define \%a {{ab{cd}}
  echo \fsubstring(\%a)
  ab{cd

13.7. Defining Variables on the C-Kermit Command Line

To define variables on the C-Kermit command line, use the -C command-line
option with one or more DEFINE or ASSIGN commands.  Note that the C-Kermit
command line must cope with the quoting rules of your shell.  Examples:

  kermit -C "define \\%a foo, define phonenumber 7654321"

In this case we follow UNIX quoting rules by doubling the backslash.  Once
C-Kermit starts, the \%a and \m(phonenumber) variables are defined as
indicated and can be used in the normal way.

In DOS or Windows or OS/2 the command would be:

  kermit -C "define \%%a foo, define phonenumber 7654321"

Here we need to double the percent sign rather than the backslash because
of DOS shell quoting rules.

13.8. Per-Character Echo Check with the OUTPUT Command

Sometimes the OUTPUT command must be used to send commands or data to a device
in "echoplex" mode, meaning that characters must be sent one at a time, and
the next character can not be sent until the echo from the previous one has
been received.  For example, a certain PBX might have this characteristic.
Let's say a Kermit script is used to program the PBX.  If characters are sent
too fast, they can be lost.  It would seem that the command:

  SET OUTPUT PACING <milliseconds>

could be used to take care of this, but the pacing interval is constant and
must be set large enough to allow even the slowest echo to finish.  If the
script is large (an actual example is 14,000 lines long), this can cause it
to take hours longer than it needs to.

Here is a macro you can use to OUTPUT a string in an Echoplex environment:

  define XOUTPUT {
      local \%c \%i
      set output pacing 0
      for \%i 1 \flen(\%*) 1 {
	  asg \%c \fsubstr(\%*,\%i,1)
          output \%c
	  input 2 \%c
      }
  }

C-Kermit 7.0 or later is required.

It sends one character at a time and then waits up to 2 seconds for the
character to be echoed back, but continues to the next character as soon
as the echo appears, so no time is wasted.  You can add an IF FAIL clause
after the INPUT in case you want to do something special about failure
to detect an echo within the timeout period.  Obviously you can also change
the 2-second limit, and adjust the script in any other desired way.

13.9. Other...

Escape sequences (or any strings that contain control characters) can't be
used as labels, GOTO targets, or SWITCH cases.

(End of CKCBWR.TXT)