NAME¶
Net::Telnet - interact with TELNET port or other TCP ports
SYNOPSIS¶
"use Net::Telnet ();"
see METHODS section below
DESCRIPTION¶
Net::Telnet allows you to make client connections to a TCP port and do network
I/O, especially to a port using the TELNET protocol. Simple I/O methods such
as print, get, and getline are provided. More sophisticated interactive
features are provided because connecting to a TELNET port ultimately means
communicating with a program designed for human interaction. These interactive
features include the ability to specify a time-out and to wait for patterns to
appear in the input stream, such as the prompt from a shell.
Other reasons to use this module than strictly with a TELNET port are:
- •
- You're not familiar with sockets and you want a simple way
to make client connections to TCP services.
- •
- You want to be able to specify your own time-out while
connecting, reading, or writing.
- •
- You're communicating with an interactive program at the
other end of some socket or pipe and you want to wait for certain patterns
to appear.
Here's an example that prints who's logged-on to the remote host sparky. In
addition to a username and password, you must also know the user's shell
prompt, which for this example is "bash$"
use Net::Telnet ();
$t = new Net::Telnet (Timeout => 10,
Prompt => '/bash\$ $/');
$t->open("sparky");
$t->login($username, $passwd);
@lines = $t->cmd("who");
print @lines;
More examples are in the
EXAMPLES section below.
Usage questions should be directed to the Usenet newsgroup
comp.lang.perl.modules.
Contact me, Jay Rogers <jay@rgrs.com>, if you find any bugs or have
suggestions for improvement.
What To Know Before Using
- •
- All output is flushed while all input is buffered. Each
object contains its own input buffer.
- •
- The output record separator for "print()" and
"cmd()" is set to "\n" by default, so that you don't
have to append all your commands with a newline. To avoid printing a
trailing "\n" use "put()" or set the
output_record_separator to "".
- •
- The methods "login()" and "cmd()" use
the prompt setting in the object to determine when a login or
remote command is complete. Those methods will fail with a time-out if you
don't set the prompt correctly.
- •
- Use a combination of "print()" and
"waitfor()" as an alternative to "login()" or
"cmd()" when they don't do what you want.
- •
- Errors such as timing-out are handled according to the
error mode action. The default action is to print an error message to
standard error and have the program die. See the "errmode()"
method for more information.
- •
- When constructing the match operator argument for
"prompt()" or "waitfor()", always use single quotes
instead of double quotes to avoid unexpected backslash interpretation
(e.g. '/bash\$ $/'). If you're constructing a DOS like file path, you'll
need to use four backslashes to represent one (e.g.
'/c:\\\\users\\\\bill>$/i').
Of course don't forget about regexp metacharacters like ".",
"[", or "$". You'll only need a single backslash to
quote them. The anchor metacharacters "^" and "$"
refer to positions in the input buffer. To avoid matching characters read
that look like a prompt, it's a good idea to end your prompt pattern with
the "$" anchor. That way the prompt will only match if it's the
last thing read.
- •
- In the input stream, each sequence of carriage
return and line feed (i.e. "\015\012" or CR
LF) is converted to "\n". In the output stream, each occurrence
of "\n" is converted to a sequence of CR LF. See
"binmode()" to change the behavior. TCP protocols typically use
the ASCII sequence, carriage return and line feed to designate a
newline.
- •
- Timing-out while making a connection is disabled for
machines that don't support the "alarm()" function. Most notably
these include MS-Windows machines.
- •
- You'll need to be running at least Perl version 5.002 to
use this module. This module does not require any libraries that don't
already come with a standard Perl distribution.
If you have the IO:: libraries installed (they come standard with perl5.004
and later) then IO::Socket::INET is used as a base class, otherwise
FileHandle is used.
- •
- Contact me, Jay Rogers <jay@rgrs.com>, if you find
any bugs or have suggestions for improvement.
Debugging
The typical usage bug causes a time-out error because you've made incorrect
assumptions about what the remote side actually sends. The easiest way to
reconcile what the remote side sends with your expectations is to use
"input_log()" or "dump_log()".
"dump_log()" allows you to see the data being sent from the remote
side before any translation is done, while "input_log()" shows you
the results after translation. The translation includes converting end of line
characters, removing and responding to TELNET protocol commands in the data
stream.
Style of Named Parameters
Two different styles of named parameters are supported. This document only shows
the IO:: style:
Net::Telnet->new(Timeout => 20);
however the dash-option style is also allowed:
Net::Telnet->new(-timeout => 20);
Connecting to a Remote MS-Windows Machine
By default MS-Windows doesn't come with a TELNET server. However third party
TELNET servers are available. Unfortunately many of these servers falsely
claim to be a TELNET server. This is especially true of the so-called
"Microsoft Telnet Server" that comes installed with some newer
versions MS-Windows.
When a TELNET server first accepts a connection, it must use the ASCII control
characters carriage-return and line-feed to start a new line (see RFC854). A
server like the "Microsoft Telnet Server" that doesn't do this,
isn't a TELNET server. These servers send ANSI terminal escape sequences to
position to a column on a subsequent line and to even position while writing
characters that are adjacent to each other. Worse, when sending output these
servers resend previously sent command output in a misguided attempt to
display an entire terminal screen.
Connecting Net::Telnet to one of these false TELNET servers makes your job of
parsing command output very difficult. It's better to replace a false TELNET
server with a real TELNET server. The better TELNET servers for MS-Windows
allow you to avoid the ANSI escapes by turning off something some of them call
console mode.
METHODS¶
In the calling sequences below, square brackets
[] represent optional
parameters.
- new - create a new Net::Telnet object
-
$obj = new Net::Telnet ([$host]);
$obj = new Net::Telnet ([Binmode => $mode,]
[Cmd_remove_mode => $mode,]
[Dump_Log => $filename,]
[Errmode => $errmode,]
[Fhopen => $filehandle,]
[Host => $host,]
[Input_log => $file,]
[Input_record_separator => $chars,]
[Option_log => $file,]
[Ors => $chars,]
[Output_log => $file,]
[Output_record_separator => $chars,]
[Port => $port,]
[Prompt => $matchop,]
[Rs => $chars,]
[Telnetmode => $mode,]
[Timeout => $secs,]);
This is the constructor for Net::Telnet objects. A new object is returned on
success, the error mode action is performed on failure - see
"errmode()". The optional arguments are short-cuts to methods of
the same name.
If the $host argument is given then the object is opened by
connecting to TCP $port on $host. Also see
"open()". The new object returned is given the following
defaults in the absence of corresponding named parameters:
- *
- The default Host is "localhost"
- *
- The default Port is 23
- *
- The default Prompt is '/[\$%#>] $/'
- *
- The default Timeout is 10
- *
- The default Errmode is "die"
- *
- The default Output_record_separator is
"\n". Note that Ors is synonymous with
Output_record_separator.
- *
- The default Input_record_separator is
"\n". Note that Rs is synonymous with
Input_record_separator.
- *
- The default Binmode is 0, which means do newline
translation.
- *
- The default Telnetmode is 1, which means respond to
TELNET commands in the data stream.
- *
- The default Cmd_remove_mode is "auto"
- *
- The defaults for Dump_log, Input_log,
Option_log, and Output_log are "", which means
that logging is turned-off.
- binmode - toggle newline translation
-
$mode = $obj->binmode;
$prev = $obj->binmode($mode);
This method controls whether or not sequences of carriage returns and line
feeds (CR LF or more specifically "\015\012") are translated. By
default they are translated (i.e. binmode is 0).
If no argument is given, the current mode is returned.
If $mode is 1 then binmode is on and newline translation is
not done.
If $mode is 0 then binmode is off and newline translation is
done. In the input stream, each sequence of CR LF is converted to
"\n" and in the output stream, each occurrence of "\n"
is converted to a sequence of CR LF.
Note that input is always buffered. Changing binmode doesn't effect what's
already been read into the buffer. Output is not buffered and changing
binmode will have an immediate effect.
- break - send TELNET break character
-
$ok = $obj->break;
This method sends the TELNET break character. This character is provided
because it's a signal outside the ASCII character set which is currently
given local meaning within many systems. It's intended to indicate that
the Break Key or the Attention Key was hit.
This method returns 1 on success, or performs the error mode action on
failure.
- buffer - scalar reference to object's input
buffer
-
$ref = $obj->buffer;
This method returns a scalar reference to the input buffer for $obj.
Data in the input buffer is data that has been read from the remote side
but has yet to be read by the user. Modifications to the input buffer are
returned by a subsequent read.
- buffer_empty - discard all data in object's input
buffer
-
$obj->buffer_empty;
This method removes all data in the input buffer for $obj.
- close - close object
-
$ok = $obj->close;
This method closes the socket, file, or pipe associated with the object. It
always returns a value of 1.
- cmd - issue command and retrieve output
-
$ok = $obj->cmd($string);
$ok = $obj->cmd(String => $string,
[Output => $ref,]
[Cmd_remove_mode => $mode,]
[Errmode => $mode,]
[Input_record_separator => $chars,]
[Ors => $chars,]
[Output_record_separator => $chars,]
[Prompt => $match,]
[Rs => $chars,]
[Timeout => $secs,]);
@output = $obj->cmd($string);
@output = $obj->cmd(String => $string,
[Output => $ref,]
[Cmd_remove_mode => $mode,]
[Errmode => $mode,]
[Input_record_separator => $chars,]
[Ors => $chars,]
[Output_record_separator => $chars,]
[Prompt => $match,]
[Rs => $chars,]
[Timeout => $secs,]);
This method sends the command $string, and reads the characters sent
back by the command up until and including the matching prompt. It's
assumed that the program to which you're sending is some kind of command
prompting interpreter such as a shell.
The command $string is automatically appended with the
output_record_separator, By default that's "\n". This is similar
to someone typing a command and hitting the return key. Set the
output_record_separator to change this behavior.
In a scalar context, the characters read from the remote side are discarded
and 1 is returned on success. On time-out, eof, or other failures, the
error mode action is performed. See "errmode()".
In a list context, just the output generated by the command is returned, one
line per element. In other words, all the characters in between the echoed
back command string and the prompt are returned. If the command happens to
return no output, a list containing one element, the empty string is
returned. This is so the list will indicate true in a boolean context. On
time-out, eof, or other failures, the error mode action is performed. See
"errmode()".
The characters that matched the prompt may be retrieved using
"last_prompt()".
Many command interpreters echo back the command sent. In most situations,
this method removes the first line returned from the remote side (i.e. the
echoed back command). See "cmd_remove_mode()" for more control
over this feature.
Use "dump_log()" to debug when this method keeps timing-out and
you don't think it should.
Consider using a combination of "print()" and
"waitfor()" as an alternative to this method when it doesn't do
what you want, e.g. the command you send prompts for input.
The Output named parameter provides an alternative method of
receiving command output. If you pass a scalar reference, all the output
(even if it contains multiple lines) is returned in the referenced scalar.
If you pass an array or hash reference, the lines of output are returned
in the referenced array or hash. You can use
"input_record_separator()" to change the notion of what
separates a line.
Optional named parameters are provided to override the current settings of
cmd_remove_mode, errmode, input_record_separator, ors,
output_record_separator, prompt, rs, and timeout. Rs is synonymous with
input_record_separator and ors is synonymous with
output_record_separator.
- cmd_remove_mode - toggle removal of echoed
commands
-
$mode = $obj->cmd_remove_mode;
$prev = $obj->cmd_remove_mode($mode);
This method controls how to deal with echoed back commands in the output
returned by cmd(). Typically, when you send a command to the remote
side, the first line of output returned is the command echoed back. Use
this mode to remove the first line of output normally returned by
cmd().
If no argument is given, the current mode is returned.
If $mode is 0 then the command output returned from cmd() has
no lines removed. If $mode is a positive integer, then the first
$mode lines of command output are stripped.
By default, $mode is set to "auto". Auto means that whether
or not the first line of command output is stripped, depends on whether or
not the remote side offered to echo. By default, Net::Telnet always
accepts an offer to echo by the remote side. You can change the default to
reject such an offer using "option_accept()".
A warning is printed to STDERR when attempting to set this attribute to
something that's not "auto" or a non-negative integer.
- dump_log - log all I/O in dump format
-
$fh = $obj->dump_log;
$fh = $obj->dump_log($fh);
$fh = $obj->dump_log($filename);
This method starts or stops dump format logging of all the object's input
and output. The dump format shows the blocks read and written in a
hexadecimal and printable character format. This method is useful when
debugging, however you might want to first try "input_log()" as
it's more readable.
If no argument is given, the current log filehandle is returned. An empty
string indicates logging is off.
To stop logging, use an empty string as an argument.
If an open filehandle is given, it is used for logging and returned.
Otherwise, the argument is assumed to be the name of a file, the file is
opened and a filehandle to it is returned. If the file can't be opened for
writing, the error mode action is performed.
- eof - end of file indicator
-
$eof = $obj->eof;
This method returns 1 if end of file has been read, otherwise it returns an
empty string. Because the input is buffered this isn't the same thing as
$obj has closed. In other words $obj can be closed but there
still can be stuff in the buffer to be read. Under this condition you can
still read but you won't be able to write.
- errmode - define action to be performed on
error
-
$mode = $obj->errmode;
$prev = $obj->errmode($mode);
This method gets or sets the action used when errors are encountered using
the object. The first calling sequence returns the current error mode. The
second calling sequence sets it to $mode and returns the previous
mode. Valid values for $mode are "die" (the default),
"return", a coderef, or an arrayref.
When mode is "die" and an error is encountered using the object,
then an error message is printed to standard error and the program dies.
When mode is "return" then the method generating the error places
an error message in the object and returns an undefined value in a scalar
context and an empty list in list context. The error message may be
obtained using "errmsg()".
When mode is a coderef, then when an error is encountered
coderef is called with the error message as its first argument.
Using this mode you may have your own subroutine handle errors. If
coderef itself returns then the method generating the error returns
undefined or an empty list depending on context.
When mode is an arrayref, the first element of the array must be a
coderef. Any elements that follow are the arguments to
coderef. When an error is encountered, the coderef is called
with its arguments. Using this mode you may have your own subroutine
handle errors. If the coderef itself returns then the method
generating the error returns undefined or an empty list depending on
context.
A warning is printed to STDERR when attempting to set this attribute to
something that's not "die", "return", a
coderef, or an arrayref whose first element isn't a
coderef.
- errmsg - most recent error message
-
$msg = $obj->errmsg;
$prev = $obj->errmsg(@msgs);
The first calling sequence returns the error message associated with the
object. The empty string is returned if no error has been encountered yet.
The second calling sequence sets the error message for the object to the
concatenation of @msgs and returns the previous error message.
Normally, error messages are set internally by a method when an error is
encountered.
- error - perform the error mode action
-
$obj->error(@msgs);
This method concatenates @msgs into a string and places it in the
object as the error message. Also see "errmsg()". It then
performs the error mode action. Also see "errmode()".
If the error mode doesn't cause the program to die, then an undefined value
or an empty list is returned depending on the context.
This method is primarily used by this class or a sub-class to perform the
user requested action when an error is encountered.
- fhopen - use already open filehandle for I/O
-
$ok = $obj->fhopen($fh);
This method associates the open filehandle $fh with $obj for
further I/O. Filehandle $fh must already be opened.
Suppose you want to use the features of this module to do I/O to something
other than a TCP port, for example STDIN or a filehandle opened to read
from a process. Instead of opening the object for I/O to a TCP port by
using "open()" or "new()", call this method instead.
The value 1 is returned success, the error mode action is performed on
failure.
- get - read block of data
-
$data = $obj->get([Binmode => $mode,]
[Errmode => $errmode,]
[Telnetmode => $mode,]
[Timeout => $secs,]);
This method reads a block of data from the object and returns it along with
any buffered data. If no buffered data is available to return, it will
wait for data to read using the timeout specified in the object. You can
override that timeout using $secs. Also see "timeout()".
If buffered data is available to return, it also checks for a block of
data that can be immediately read.
On eof an undefined value is returned. On time-out or other failures, the
error mode action is performed. To distinguish between eof or an error
occurring when the error mode is not set to "die", use
"eof()".
Optional named parameters are provided to override the current settings of
binmode, errmode, telnetmode, and timeout.
- getline - read next line
-
$line = $obj->getline([Binmode => $mode,]
[Errmode => $errmode,]
[Input_record_separator => $chars,]
[Rs => $chars,]
[Telnetmode => $mode,]
[Timeout => $secs,]);
This method reads and returns the next line of data from the object. You can
use "input_record_separator()" to change the notion of what
separates a line. The default is "\n". If a line isn't
immediately available, this method blocks waiting for a line or a
time-out.
On eof an undefined value is returned. On time-out or other failures, the
error mode action is performed. To distinguish between eof or an error
occurring when the error mode is not set to "die", use
"eof()".
Optional named parameters are provided to override the current settings of
binmode, errmode, input_record_separator, rs, telnetmode, and timeout. Rs
is synonymous with input_record_separator.
- getlines - read next lines
-
@lines = $obj->getlines([Binmode => $mode,]
[Errmode => $errmode,]
[Input_record_separator => $chars,]
[Rs => $chars,]
[Telnetmode => $mode,]
[Timeout => $secs,]
[All => $boolean,]);
This method reads and returns all the lines of data from the object until
end of file is read. You can use "input_record_separator()" to
change the notion of what separates a line. The default is "\n".
A time-out error occurs if all the lines can't be read within the time-out
interval. See "timeout()".
The behavior of this method was changed in version 3.03. Prior to version
3.03 this method returned just the lines available from the next read. To
get that old behavior, use the optional named parameter All and set
$boolean to "" or 0.
If only eof is read then an empty list is returned. On time-out or other
failures, the error mode action is performed. Use "eof()" to
distinguish between reading only eof or an error occurring when the error
mode is not set to "die".
Optional named parameters are provided to override the current settings of
binmode, errmode, input_record_separator, rs, telnetmode, and timeout. Rs
is synonymous with input_record_separator.
- host - name of remote host
-
$host = $obj->host;
$prev = $obj->host($host);
This method designates the remote host for "open()". With no
argument it returns the current host name set in the object. With an
argument it sets the current host name to $host and returns the
previous host name. You may indicate the remote host using either a
hostname or an IP address.
The default value is "localhost". It may also be set by
"open()" or "new()".
- input_log - log all input
-
$fh = $obj->input_log;
$fh = $obj->input_log($fh);
$fh = $obj->input_log($filename);
This method starts or stops logging of input. This is useful when debugging.
Also see "dump_log()". Because most command interpreters echo
back commands received, it's likely all your output will also be in this
log. Note that input logging occurs after newline translation. See
"binmode()" for details on newline translation.
If no argument is given, the log filehandle is returned. An empty string
indicates logging is off.
To stop logging, use an empty string as an argument.
If an open filehandle is given, it is used for logging and returned.
Otherwise, the argument is assumed to be the name of a file, the file is
opened for logging and a filehandle to it is returned. If the file can't
be opened for writing, the error mode action is performed.
- input_record_separator - input line delimiter
-
$chars = $obj->input_record_separator;
$prev = $obj->input_record_separator($chars);
This method designates the line delimiter for input. It's used with
"getline()", "getlines()", and "cmd()" to
determine lines in the input.
With no argument this method returns the current input record separator set
in the object. With an argument it sets the input record separator to
$chars and returns the previous value. Note that $chars must
have length.
A warning is printed to STDERR when attempting to set this attribute to a
string with no length.
- last_prompt - last prompt read
-
$string = $obj->last_prompt;
$prev = $obj->last_prompt($string);
With no argument this method returns the last prompt read by cmd() or
login(). See "prompt()". With an argument it sets the
last prompt read to $string and returns the previous value.
Normally, only internal methods set the last prompt.
- lastline - last line read
-
$line = $obj->lastline;
$prev = $obj->lastline($line);
This method retrieves the last line read from the object. This may be a
useful error message when the remote side abnormally closes the
connection. Typically the remote side will print an error message before
closing.
With no argument this method returns the last line read from the object.
With an argument it sets the last line read to $line and returns
the previous value. Normally, only internal methods set the last
line.
- login - perform standard login
-
$ok = $obj->login($username, $password);
$ok = $obj->login(Name => $username,
Password => $password,
[Errmode => $mode,]
[Prompt => $match,]
[Timeout => $secs,]);
This method performs a standard login by waiting for a login prompt and
responding with $username, then waiting for the password prompt and
responding with $password, and then waiting for the command
interpreter prompt. If any of those prompts sent by the remote side don't
match what's expected, this method will time-out, unless timeout is turned
off.
Login prompt must match either of these case insensitive patterns:
/login[: ]*$/i
/username[: ]*$/i
Password prompt must match this case insensitive pattern:
/password[: ]*$/i
The command interpreter prompt must match the current setting of prompt. See
"prompt()".
Use "dump_log()" to debug when this method keeps timing-out and
you don't think it should.
Consider using a combination of "print()" and
"waitfor()" as an alternative to this method when it doesn't do
what you want, e.g. the remote host doesn't prompt for a username.
On success, 1 is returned. On time out, eof, or other failures, the error
mode action is performed. See "errmode()".
Optional named parameters are provided to override the current settings of
errmode, prompt, and timeout.
- max_buffer_length - maximum size of input
buffer
-
$len = $obj->max_buffer_length;
$prev = $obj->max_buffer_length($len);
This method designates the maximum size of the input buffer. An error is
generated when a read causes the buffer to exceed this limit. The default
value is 1,048,576 bytes (1MB). The input buffer can grow much larger than
the block size when you continuously read using "getline()" or
"waitfor()" and the data stream contains no newlines or matching
waitfor patterns.
With no argument, this method returns the current maximum buffer length set
in the object. With an argument it sets the maximum buffer length to
$len and returns the previous value. Values of $len smaller
than 512 will be adjusted to 512.
A warning is printed to STDERR when attempting to set this attribute to
something that isn't a positive integer.
- ofs - field separator for print
-
$chars = $obj->ofs
$prev = $obj->ofs($chars);
This method is synonymous with "output_field_separator()".
- open - connect to port on remote host
-
$ok = $obj->open($host);
$ok = $obj->open([Host => $host,]
[Port => $port,]
[Errmode => $mode,]
[Timeout => $secs,]);
This method opens a TCP connection to $port on $host. If
either argument is missing then the current value of "host()" or
"port()" is used. Optional named parameters are provided to
override the current setting of errmode and timeout.
On success 1 is returned. On time-out or other connection failures, the
error mode action is performed. See "errmode()".
Time-outs don't work for this method on machines that don't implement
SIGALRM - most notably MS-Windows machines. For those machines, an error
is returned when the system reaches its own time-out while trying to
connect.
A side effect of this method is to reset the alarm interval associated with
SIGALRM.
- option_accept - indicate willingness to accept a
TELNET option
-
$fh = $obj->option_accept([Do => $telopt,]
[Dont => $telopt,]
[Will => $telopt,]
[Wont => $telopt,]);
This method is used to indicate whether to accept or reject an offer to
enable a TELNET option made by the remote side. If you're using Do
or Will to indicate a willingness to enable, then a notification
callback must have already been defined by a prior call to
"option_callback()". See "option_callback()" for
details on receiving enable/disable notification of a TELNET option.
You can give multiple Do, Dont, Will, or Wont
arguments for different TELNET options in the same call to this method.
The following example describes the meaning of the named parameters. A
TELNET option, such as "TELOPT_ECHO" used below, is an integer
constant that you can import from Net::Telnet. See the source in file
Telnet.pm for the complete list.
- *
- Do => "TELOPT_ECHO"
- *
- we'll accept an offer to enable the echo option on the
local side
- *
- Dont => "TELOPT_ECHO"
- *
- we'll reject an offer to enable the echo option on the
local side
- *
- Will => "TELOPT_ECHO"
- *
- we'll accept an offer to enable the echo option on the
remote side
- *
- Wont => "TELOPT_ECHO"
- *
- we'll reject an offer to enable the echo option on the
remote side
- *
- Use "option_send()" to send a request to the
remote side to enable or disable a particular TELNET option.
- option_callback - define the option negotiation
callback
-
$coderef = $obj->option_callback;
$prev = $obj->option_callback($coderef);
This method defines the callback subroutine that's called when a TELNET
option is enabled or disabled. Once defined, the option_callback
may not be undefined. However, calling this method with a different
$coderef changes it.
A warning is printed to STDERR when attempting to set this attribute to
something that isn't a coderef.
Here are the circumstances that invoke $coderef:
- *
- An option becomes enabled because the remote side requested
an enable and "option_accept()" had been used to arrange that it
be accepted.
- *
- The remote side arbitrarily decides to disable an option
that is currently enabled. Note that Net::Telnet always accepts a request
to disable from the remote side.
- *
- "option_send()" was used to send a request to
enable or disable an option and the response from the remote side has just
been received. Note, that if a request to enable is rejected then
$coderef is still invoked even though the option didn't
change.
- *
- Here are the arguments passed to &$coderef:
&$coderef($obj, $option, $is_remote,
$is_enabled, $was_enabled, $buf_position);
- *
- 1. $obj is the Net::Telnet object
- *
- 2. $option is the TELNET option. Net::Telnet exports
constants for the various TELNET options which just equate to an
integer.
- *
- 3. $is_remote is a boolean indicating for which side
the option applies.
- *
- 4. $is_enabled is a boolean indicating the option is
enabled or disabled
- *
- 5. $was_enabled is a boolean indicating the option
was previously enabled or disabled
- *
- 6. $buf_position is an integer indicating the
position in the object's input buffer where the option takes effect. See
"buffer()" to access the object's input buffer.
- option_log - log all TELNET options sent or
received
-
$fh = $obj->option_log;
$fh = $obj->option_log($fh);
$fh = $obj->option_log($filename);
This method starts or stops logging of all TELNET options being sent or
received. This is useful for debugging when you send options via
"option_send()" or you arrange to accept option requests from
the remote side via "option_accept()". Also see
"dump_log()".
If no argument is given, the log filehandle is returned. An empty string
indicates logging is off.
To stop logging, use an empty string as an argument.
If an open filehandle is given, it is used for logging and returned.
Otherwise, the argument is assumed to be the name of a file, the file is
opened for logging and a filehandle to it is returned. If the file can't
be opened for writing, the error mode action is performed.
- option_send - send TELNET option negotiation
request
-
$ok = $obj->option_send([Do => $telopt,]
[Dont => $telopt,]
[Will => $telopt,]
[Wont => $telopt,]
[Async => $boolean,]);
This method is not yet implemented. Look for it in a future version.
- option_state - get current state of a TELNET
option
-
$hashref = $obj->option_state($telopt);
This method returns a hashref containing a copy of the current state of
TELNET option $telopt.
Here are the values returned in the hash:
- *
- $hashref->{remote_enabled}
- *
- boolean that indicates if the option is enabled on the
remote side.
- *
- $hashref->{remote_enable_ok}
- *
- boolean that indicates if it's ok to accept an offer to
enable this option on the remote side.
- *
- $hashref->{remote_state}
- *
- string used to hold the internal state of option
negotiation for this option on the remote side.
- *
- $hashref->{local_enabled}
- *
- boolean that indicates if the option is enabled on the
local side.
- *
- $hashref->{local_enable_ok}
- *
- boolean that indicates if it's ok to accept an offer to
enable this option on the local side.
- *
- $hashref->{local_state}
- *
- string used to hold the internal state of option
negotiation for this option on the local side.
- ors - output line delimiter
-
$chars = $obj->ors;
$prev = $obj->ors($chars);
This method is synonymous with "output_record_separator()".
- output_field_separator - field separator for
print
-
$chars = $obj->output_field_separator;
$prev = $obj->output_field_separator($chars);
This method designates the output field separator for "print()".
Ordinarily the print method simply prints out the comma separated fields
you specify. Set this to specify what's printed between fields.
With no argument this method returns the current output field separator set
in the object. With an argument it sets the output field separator to
$chars and returns the previous value.
By default it's set to an empty string.
- output_log - log all output
-
$fh = $obj->output_log;
$fh = $obj->output_log($fh);
$fh = $obj->output_log($filename);
This method starts or stops logging of output. This is useful when
debugging. Also see "dump_log()". Because most command
interpreters echo back commands received, it's likely all your output
would also be in an input log. See "input_log()". Note that
output logging occurs before newline translation. See
"binmode()" for details on newline translation.
If no argument is given, the log filehandle is returned. An empty string
indicates logging is off.
To stop logging, use an empty string as an argument.
If an open filehandle is given, it is used for logging and returned.
Otherwise, the argument is assumed to be the name of a file, the file is
opened for logging and a filehandle to it is returned. If the file can't
be opened for writing, the error mode action is performed.
- output_record_separator - output line delimiter
-
$chars = $obj->output_record_separator;
$prev = $obj->output_record_separator($chars);
This method designates the output line delimiter for "print()" and
"cmd()". Set this to specify what's printed at the end of
"print()" and "cmd()".
The output record separator is set to "\n" by default, so there's
no need to append all your commands with a newline. To avoid printing the
output_record_separator use "put()" or set the
output_record_separator to an empty string.
With no argument this method returns the current output record separator set
in the object. With an argument it sets the output record separator to
$chars and returns the previous value.
- port - remote port
-
$port = $obj->port;
$prev = $obj->port($port);
This method designates the remote TCP port. With no argument this method
returns the current port number. With an argument it sets the current port
number to $port and returns the previous port. If $port is a
TCP service name, then it's first converted to a port number using the
perl function "getservbyname()".
The default value is 23. It may also be set by "open()" or
"new()".
A warning is printed to STDERR when attempting to set this attribute to
something that's not a positive integer or a valid TCP service name.
- print - write to object
-
$ok = $obj->print(@list);
This method writes @list followed by the
output_record_separator to the open object and returns 1 if all
data was successfully written. On time-out or other failures, the error
mode action is performed. See "errmode()".
By default, the "output_record_separator()" is set to
"\n" so all your commands automatically end with a newline. In
most cases your output is being read by a command interpreter which won't
accept a command until newline is read. This is similar to someone typing
a command and hitting the return key. To avoid printing a trailing
"\n" use "put()" instead or set the
output_record_separator to an empty string.
On failure, it's possible that some data was written. If you choose to try
and recover from a print timing-out, use "print_length()" to
determine how much was written before the error occurred.
You may also use the output field separator to print a string between the
list elements. See "output_field_separator()".
- print_length - number of bytes written by print
-
$num = $obj->print_length;
This returns the number of bytes successfully written by the most recent
"print()" or "put()".
- prompt - pattern to match a prompt
-
$matchop = $obj->prompt;
$prev = $obj->prompt($matchop);
This method sets the pattern used to find a prompt in the input stream. It
must be a string representing a valid perl pattern match operator. The
methods "login()" and "cmd()" try to read until
matching the prompt. They will fail with a time-out error if the pattern
you've chosen doesn't match what the remote side sends.
With no argument this method returns the prompt set in the object. With an
argument it sets the prompt to $matchop and returns the previous
value.
The default prompt is '/[\$%#>] $/'
Always use single quotes, instead of double quotes, to construct
$matchop (e.g. '/bash\$ $/'). If you're constructing a DOS like
file path, you'll need to use four backslashes to represent one (e.g.
'/c:\\\\users\\\\bill>$/i').
Of course don't forget about regexp metacharacters like ".",
"[", or "$". You'll only need a single backslash to
quote them. The anchor metacharacters "^" and "$"
refer to positions in the input buffer.
A warning is printed to STDERR when attempting to set this attribute with a
match operator missing its opening delimiter.
- put - write to object
-
$ok = $obj->put($string);
$ok = $obj->put(String => $string,
[Binmode => $mode,]
[Errmode => $errmode,]
[Telnetmode => $mode,]
[Timeout => $secs,]);
This method writes $string to the opened object and returns 1 if all
data was successfully written. This method is like "print()"
except that it doesn't write the trailing output_record_separator
("\n" by default). On time-out or other failures, the error mode
action is performed. See "errmode()".
On failure, it's possible that some data was written. If you choose to try
and recover from a put timing-out, use "print_length()" to
determine how much was written before the error occurred.
Optional named parameters are provided to override the current settings of
binmode, errmode, telnetmode, and timeout.
- rs - input line delimiter
-
$chars = $obj->rs;
$prev = $obj->rs($chars);
This method is synonymous with "input_record_separator()".
- telnetmode - turn off/on telnet command
interpretation
-
$mode = $obj->telnetmode;
$prev = $obj->telnetmode($mode);
This method controls whether or not TELNET commands in the data stream are
recognized and handled. The TELNET protocol uses certain character
sequences sent in the data stream to control the session. If the port
you're connecting to isn't using the TELNET protocol, then you should turn
this mode off. The default is on.
If no argument is given, the current mode is returned.
If $mode is 0 then telnet mode is off. If $mode is 1 then
telnet mode is on.
- timed_out - time-out indicator
-
$boolean = $obj->timed_out;
$prev = $obj->timed_out($boolean);
This method indicates if a previous read, write, or open method timed-out.
Remember that timing-out is itself an error. To be able to invoke
"timed_out()" after a time-out error, you'd have to change the
default error mode to something other than "die". See
"errmode()".
With no argument this method returns 1 if the previous method timed-out.
With an argument it sets the indicator. Normally, only internal methods
set this indicator.
- timeout - I/O time-out interval
-
$secs = $obj->timeout;
$prev = $obj->timeout($secs);
This method sets the timeout interval that's used when performing I/O or
connecting to a port. When a method doesn't complete within the timeout
interval then it's an error and the error mode action is performed.
A timeout may be expressed as a relative or absolute value. If $secs
is greater than or equal to the time the program started, as determined by
$^T, then it's an absolute time value for when time-out occurs. The perl
function "time()" may be used to obtain an absolute time value.
For a relative time-out value less than $^T, time-out happens $secs
from when the method begins.
If $secs is 0 then time-out occurs if the data cannot be immediately
read or written. Use the undefined value to turn off timing-out
completely.
With no argument this method returns the timeout set in the object. With an
argument it sets the timeout to $secs and returns the previous
value. The default timeout value is 10 seconds.
A warning is printed to STDERR when attempting to set this attribute to
something that's not an "undef" or a non-negative integer.
- waitfor - wait for pattern in the input
-
$ok = $obj->waitfor($matchop);
$ok = $obj->waitfor([Match => $matchop,]
[String => $string,]
[Binmode => $mode,]
[Errmode => $errmode,]
[Telnetmode => $mode,]
[Timeout => $secs,]);
($prematch, $match) = $obj->waitfor($matchop);
($prematch, $match) = $obj->waitfor([Match => $matchop,]
[String => $string,]
[Binmode => $mode,]
[Errmode => $errmode,]
[Telnetmode => $mode,]
[Timeout => $secs,]);
This method reads until a pattern match or string is found in the input
stream. All the characters before and including the match are removed from
the input stream.
In a list context the characters before the match and the matched characters
are returned in $prematch and $match. In a scalar context,
the matched characters and all characters before it are discarded and 1 is
returned on success. On time-out, eof, or other failures, for both list
and scalar context, the error mode action is performed. See
"errmode()".
You can specify more than one pattern or string by simply providing multiple
Match and/or String named parameters. A $matchop must
be a string representing a valid Perl pattern match operator. The
$string is just a substring to find in the input stream.
Use "dump_log()" to debug when this method keeps timing-out and
you don't think it should.
An optional named parameter is provided to override the current setting of
timeout.
To avoid unexpected backslash interpretation, always use single quotes
instead of double quotes to construct a match operator argument for
"prompt()" and "waitfor()" (e.g. '/bash\$ $/'). If
you're constructing a DOS like file path, you'll need to use four
backslashes to represent one (e.g. '/c:\\\\users\\\\bill>$/i').
Of course don't forget about regexp metacharacters like ".",
"[", or "$". You'll only need a single backslash to
quote them. The anchor metacharacters "^" and "$"
refer to positions in the input buffer.
Optional named parameters are provided to override the current settings of
binmode, errmode, telnetmode, and timeout.
SEE ALSO¶
- RFC 854
- TELNET Protocol Specification
ftp://ftp.isi.edu/in-notes/rfc854.txt
- RFC 1143
- Q Method of Implementing TELNET Option Negotiation
ftp://ftp.isi.edu/in-notes/rfc1143.txt
- TELNET Option Assignments
- http://www.iana.org/assignments/telnet-options
EXAMPLES¶
This example gets the current weather forecast for Brainerd, Minnesota.
my ($forecast, $t);
use Net::Telnet ();
$t = new Net::Telnet;
$t->open("rainmaker.wunderground.com");
## Wait for first prompt and "hit return".
$t->waitfor('/continue:.*$/');
$t->print("");
## Wait for second prompt and respond with city code.
$t->waitfor('/city code.*$/');
$t->print("BRD");
## Read and print the first page of forecast.
($forecast) = $t->waitfor('/[ \t]+press return to continue/i');
print $forecast;
exit;
This example checks a POP server to see if you have mail.
my ($hostname, $line, $passwd, $pop, $username);
$hostname = "your_destination_host_here";
$username = "your_username_here";
$passwd = "your_password_here";
use Net::Telnet ();
$pop = new Net::Telnet (Telnetmode => 0);
$pop->open(Host => $hostname,
Port => 110);
## Read connection message.
$line = $pop->getline;
die $line unless $line =~ /^\+OK/;
## Send user name.
$pop->print("user $username");
$line = $pop->getline;
die $line unless $line =~ /^\+OK/;
## Send password.
$pop->print("pass $passwd");
$line = $pop->getline;
die $line unless $line =~ /^\+OK/;
## Request status of messages.
$pop->print("list");
$line = $pop->getline;
print $line;
exit;
Here's an example that uses the ssh program to connect to a remote host. Because
the ssh program reads and writes to its controlling terminal, the IO::Pty
module is used to create a new pseudo terminal for use by ssh. A new
Net::Telnet object is then created to read and write to that pseudo terminal.
To use the code below, substitute "changeme" with the actual host,
user, password, and command prompt.
## Main program.
{
my ($pty, $ssh, @lines);
my $host = "changeme";
my $user = "changeme";
my $password = "changeme";
my $prompt = '/changeme:~> $/';
## Start ssh program.
$pty = &spawn("ssh", "-l", $user, $host); # spawn() defined below
## Create a Net::Telnet object to perform I/O on ssh's tty.
use Net::Telnet;
$ssh = new Net::Telnet (-fhopen => $pty,
-prompt => $prompt,
-telnetmode => 0,
-cmd_remove_mode => 1,
-output_record_separator => "\r");
## Login to remote host.
$ssh->waitfor(-match => '/password: ?$/i',
-errmode => "return")
or die "problem connecting to host: ", $ssh->lastline;
$ssh->print($password);
$ssh->waitfor(-match => $ssh->prompt,
-errmode => "return")
or die "login failed: ", $ssh->lastline;
## Send command, get and print its output.
@lines = $ssh->cmd("who");
print @lines;
exit;
} # end main program
sub spawn {
my(@cmd) = @_;
my($pid, $pty, $tty, $tty_fd);
## Create a new pseudo terminal.
use IO::Pty ();
$pty = new IO::Pty
or die $!;
## Execute the program in another process.
unless ($pid = fork) { # child process
die "problem spawning program: $!\n" unless defined $pid;
## Disassociate process from existing controlling terminal.
use POSIX ();
POSIX::setsid
or die "setsid failed: $!";
## Associate process with a new controlling terminal.
$tty = $pty->slave;
$tty_fd = $tty->fileno;
close $pty;
## Make stdio use the new controlling terminal.
open STDIN, "<&$tty_fd" or die $!;
open STDOUT, ">&$tty_fd" or die $!;
open STDERR, ">&STDOUT" or die $!;
close $tty;
## Execute requested program.
exec @cmd
or die "problem executing $cmd[0]\n";
} # end child process
$pty;
} # end sub spawn
Here's an example that changes a user's login password. Because the passwd
program always prompts for passwords on its controlling terminal, the IO::Pty
module is used to create a new pseudo terminal for use by passwd. A new
Net::Telnet object is then created to read and write to that pseudo terminal.
To use the code below, substitute "changeme" with the actual old and
new passwords.
my ($pty, $passwd);
my $oldpw = "changeme";
my $newpw = "changeme";
## Start passwd program.
$pty = &spawn("passwd"); # spawn() defined above
## Create a Net::Telnet object to perform I/O on passwd's tty.
use Net::Telnet;
$passwd = new Net::Telnet (-fhopen => $pty,
-timeout => 2,
-output_record_separator => "\r",
-telnetmode => 0,
-cmd_remove_mode => 1);
$passwd->errmode("return");
## Send existing password.
$passwd->waitfor('/password: ?$/i')
or die "no old password prompt: ", $passwd->lastline;
$passwd->print($oldpw);
## Send new password.
$passwd->waitfor('/new password: ?$/i')
or die "bad old password: ", $passwd->lastline;
$passwd->print($newpw);
## Send new password verification.
$passwd->waitfor('/new password: ?$/i')
or die "bad new password: ", $passwd->lastline;
$passwd->print($newpw);
## Display success or failure.
$passwd->waitfor('/changed/')
or die "bad new password: ", $passwd->lastline;
print $passwd->lastline;
$passwd->close;
exit;
Here's an example you can use to down load a file of any type. The file is read
from the remote host's standard output using cat. To prevent any output
processing, the remote host's standard output is put in raw mode using the
Bourne shell. The Bourne shell is used because some shells, notably tcsh,
prevent changing tty modes. Upon completion, FTP style statistics are printed
to stderr.
my ($block, $filename, $host, $hostname, $k_per_sec, $line,
$num_read, $passwd, $prevblock, $prompt, $size, $size_bsd,
$size_sysv, $start_time, $total_time, $username);
$hostname = "your_destination_host_here";
$username = "your_username_here";
$passwd = "your_password_here";
$filename = "your_download_file_here";
## Connect and login.
use Net::Telnet ();
$host = new Net::Telnet (Timeout => 30,
Prompt => '/[%#>] $/');
$host->open($hostname);
$host->login($username, $passwd);
## Make sure prompt won't match anything in send data.
$prompt = "_funkyPrompt_";
$host->prompt("/$prompt\$/");
$host->cmd("set prompt = '$prompt'");
## Get size of file.
($line) = $host->cmd("/bin/ls -l $filename");
($size_bsd, $size_sysv) = (split ' ', $line)[3,4];
if ($size_sysv =~ /^\d+$/) {
$size = $size_sysv;
}
elsif ($size_bsd =~ /^\d+$/) {
$size = $size_bsd;
}
else {
die "$filename: no such file on $hostname";
}
## Start sending the file.
binmode STDOUT;
$host->binmode(1);
$host->print("/bin/sh -c 'stty raw; cat $filename'");
$host->getline; # discard echoed back line
## Read file a block at a time.
$num_read = 0;
$prevblock = "";
$start_time = time;
while (($block = $host->get) and ($block !~ /$prompt$/o)) {
if (length $block >= length $prompt) {
print $prevblock;
$num_read += length $prevblock;
$prevblock = $block;
}
else {
$prevblock .= $block;
}
}
$host->close;
## Print last block without trailing prompt.
$prevblock .= $block;
$prevblock =~ s/$prompt$//;
print $prevblock;
$num_read += length $prevblock;
die "error: expected size $size, received size $num_read\n"
unless $num_read == $size;
## Print totals.
$total_time = (time - $start_time) || 1;
$k_per_sec = ($size / 1024) / $total_time;
$k_per_sec = sprintf "%3.1f", $k_per_sec;
warn("$num_read bytes received in $total_time seconds ",
"($k_per_sec Kbytes/s)\n");
exit;
AUTHOR¶
Jay Rogers <jay@rgrs.com>
COPYRIGHT¶
Copyright 1997, 2000, 2002 by Jay Rogers. All rights reserved. This program is
free software; you can redistribute it and/or modify it under the same terms
as Perl itself.