Net::Telnet(3) User Contributed Perl Documentation Net::Telnet(3)
NAME
Net::Telnet - interact with TELNET port or other TCP ports
SYNOPSIS
"use Net::Telnet ();"
see METHODS or EXAMPLES sections 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. IPv6 support is available
when using perl 5.14 or later, see "family()".
Other reasons to use this module than strictly with a TELNET port are:
o You're not familiar with sockets and you want a simple way to make
client connections to TCP services.
o You want to be able to specify your own time-out while connecting,
reading, or writing.
o 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 a remote host. 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\$ $/');
$t->open($host);
$t->login($username, $passwd);
@lines = $t->cmd("who");
print @lines;
See the EXAMPLES section below for more examples.
Usage questions should be directed to the perlmonks.org discussion
group. Bugs can be viewed or reported at cpan.org on the Net::Telnet
page.
What To Know Before Using
o All output is flushed while all input is buffered. Each object
contains its own input buffer.
o 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 "".
o 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.
o Use a combination of "print()" and "waitfor()" as an alternative to
"login()" or "cmd()" when they don't do what you want.
o 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.
o 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.
o 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.
o Timing-out while making a connection is disabled for machines that
don't support the "alarm()" function. Most notably these include MS-
Windows machines.
o 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.
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,]
[Family => $family,]
[Fhopen => $filehandle,]
[Host => $host,]
[Input_log => $file,]
[Input_record_separator => $chars,]
[Localfamily => $family,]
[Localhost => $host,]
[Max_buffer_length => $len,]
[Ofs => $chars,]
[Option_log => $file,]
[Ors => $chars,]
[Output_field_separator => $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:
o The default Host is "localhost"
o The default Port is 23
o The default Family is "ipv4"
o The default Prompt is '/[\$%#>] $/'
o The default Timeout is 10
o The default Errmode is "die"
o The default Output_record_separator is "\n". Note that Ors is
synonymous with Output_record_separator.
o The default Input_record_separator is "\n". Note that Rs is
synonymous with Input_record_separator.
o The default Binmode is 0, which means do newline translation.
o The default Telnetmode is 1, which means respond to TELNET
commands in the data stream.
o The default Cmd_remove_mode is "auto"
o The defaults for Dump_log, Input_log, Option_log, and
Output_log are "", which means that logging is turned-off.
o The default Max_buffer_length is 1048576 bytes, i.e. 1 MiB.
o The default Output_field_separator is "". Note that Ofs is
synonymous with Output_field_separator.
o The default Localhost is ""
o The default Localfamily is "ipv4"
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 it is "\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 is 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 = $obj->dump_log($tiefh);
$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 log filehandle is returned. A
returned empty string indicates logging is off.
To stop logging, use an empty string as an argument. The stopped
filehandle is not closed.
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 filename is opened for logging and a filehandle to it is
returned. If the filehandle is not already opened or the filename
can't be opened for writing, the error mode action is performed.
The filehandle can be a tied filehandle.
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 is 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.
family - IP address family for remote host
$family = $obj->family;
$prev = $obj->family($family);
This method designates which IP address family "host()" refers to,
i.e. IPv4 or IPv6. IPv6 support is available when using perl 5.14
or later. With no argument it returns the current value set in the
object. With an argument it sets the current address family to
$family and returns the previous address family. Valid values are
"ipv4", "ipv6", or "any". When "any", the "host()" can be a
hostname or IP address for either IPv4 or IPv6. After connecting,
you can use "sockfamily()" to determine which IP address family was
used.
The default value is "ipv4".
The error mode action is performed when attempting to set this
attribute to something that isn't "ipv4", "ipv6", or "any". It is
also performed when attempting to set it to "ipv6" when the Socket
module is less than version 1.94 or IPv6 is not supported in the OS
as indicated by Socket::AF_INET6 not being defined.
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 or IP address of remote host
$host = $obj->host;
$prev = $obj->host($host);
This method designates the remote host for "open()". It is either
a hostname or an IP address. With no argument it returns the
current value set in the object. With an argument it sets the
current host name to $host and returns the previous value. Use
"family()" to control which IP address family, IPv4 or IPv6, host
refers to.
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 = $obj->input_log($tiefh);
$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. A
returned empty string indicates logging is off.
To stop logging, use an empty string as an argument. The stopped
filehandle is not closed.
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 filename is opened for logging and a filehandle to it is
returned. If the filehandle is not already opened or the filename
can't be opened for writing, the error mode action is performed.
The filehandle can be a tied filehandle.
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.
localfamily - IP address family for local host
$localfamily = $obj->localfamily;
$prev = $obj->localfamily($family);
This method designates which IP address family "localhost()" refers
to, i.e. IPv4 or IPv6. IPv6 support is available when using perl
5.14 or later. With no argument it returns the current value set
in the object. With an argument it sets the current local address
family to $family and returns the previous address family. Valid
values are "ipv4", "ipv6", or "any". When "any", the "localhost()"
can be a hostname or IP address for either IPv4 or IPv6.
The default value is "ipv4".
The error mode action is performed when attempting to set this
attribute to something that isn't "ipv4", "ipv6", or "any". It is
also performed when attempting to set it to "ipv6" when the Socket
module is less than version 1.94 or IPv6 is not supported in the OS
as indicated by Socket::AF_INET6 not being defined.
localhost - bind local socket to a specific network interface
$localhost = $obj->localhost;
$prev = $obj->localhost($host);
This method designates the local socket IP address for "open()".
It is either a hostname, an IP address, or a null string (i.e. "").
A null string disables this feature.
Normally the OS picks which local network interface to use. This
method is useful when the local machine has more than one network
interface and you want to bind to a specific one. With no argument
it returns the current value set in the object. With an argument
it sets the current local host name to $host and returns the
previous value. Use "localfamily()" to control which IP address
family, IPv4 or IPv6, local host refers to.
The default value is "".
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 (1 MiB). 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,]
[Family => $family,]
[Errmode => $mode,]
[Timeout => $secs,]
[Localhost => $host,]
[Localfamily => $family,]);
This method opens a TCP connection to $port on $host for the IP
address $family. If any of those arguments are missing then the
current attribute value for the object is used. Specifying Host
sets that attribute for the object. Specifying any of the other
optional named parameters overrides the current setting.
The default IP address family is "ipv4". $family may be set to
"ipv4", "ipv6", or "any". See "family()" for more details.
Localhost is used to bind to a specific local network interface.
If the object is already open, it is closed before attempting a
connection.
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.
o Do => "TELOPT_ECHO"
o we'll accept an offer to enable the echo option on the
local side
o Dont => "TELOPT_ECHO"
o we'll reject an offer to enable the echo option on the
local side
o Will => "TELOPT_ECHO"
o we'll accept an offer to enable the echo option on the
remote side
o Wont => "TELOPT_ECHO"
o we'll reject an offer to enable the echo option on the
remote side
o 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 is 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:
o An option becomes enabled because the remote side requested an
enable and "option_accept()" had been used to arrange that it
be accepted.
o 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.
o "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
$coderef is still invoked even though the option didn't change.
o Here are the arguments passed to &$coderef:
&$coderef($obj, $option, $is_remote,
$is_enabled, $was_enabled, $buf_position);
o 1. $obj is the Net::Telnet object
o 2. $option is the TELNET option. Net::Telnet exports
constants for the various TELNET options which just equate to
an integer.
o 3. $is_remote is a boolean indicating for which side the
option applies.
o 4. $is_enabled is a boolean indicating the option is enabled
or disabled
o 5. $was_enabled is a boolean indicating the option was
previously enabled or disabled
o 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 = $obj->option_log($tiefh);
$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. The stopped
filehandle is not closed.
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 filename is opened for logging and a filehandle to it is
returned. If the filehandle is not already opened or the filename
can't be opened for writing, the error mode action is performed.
The filehandle can be a tied filehandle.
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:
o $hashref->{remote_enabled}
o boolean that indicates if the option is enabled on the
remote side.
o $hashref->{remote_enable_ok}
o boolean that indicates if it's ok to accept an offer to
enable this option on the remote side.
o $hashref->{remote_state}
o string used to hold the internal state of option
negotiation for this option on the remote side.
o $hashref->{local_enabled}
o boolean that indicates if the option is enabled on the
local side.
o $hashref->{local_enable_ok}
o boolean that indicates if it's ok to accept an offer to
enable this option on the local side.
o $hashref->{local_state}
o 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 = $obj->output_log($tiefh);
$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. A
returned empty string indicates logging is off.
To stop logging, use an empty string as an argument. The stopped
filehandle is not closed.
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 filename is opened for logging and a filehandle to it is
returned. If the filehandle is not already opened or the filename
can't be opened for writing, the error mode action is performed.
The filehandle can be a tied filehandle.
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.
peerhost - IP address of the other end of the socket connection
$ipaddr = $obj->peerhost;
This method returns a string which is the IPv4 or IPv6 address the
remote socket is bound to (i.e. it is the IP address of "host()").
It returns "" when not connected.
peerport - TCP port of the other end of the socket connection
$port = $obj->peerport;
This method returns the port number which the remote socket is
bound to. It is the same as the "port()" number when connected.
It returns "" when not connected.
port - remote port
$port = $obj->port;
$prev = $obj->port($port);
This method designates the remote TCP port for "open()". 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.
The error mode action is performed when attempting to set this
attribute to something that is 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.
The error mode action is performed 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()".
sockfamily - IP address family of connected local socket
$sockfamily = $obj->sockfamily;
This method returns which IP address family "open()" used to
successfully connect. It is most useful when the requested address
"family()" for "open()" was "any". Values returned may be "ipv4",
"ipv6", or "" (when not connected).
sockhost - IP address of this end of the socket connection
$ipaddr = $obj->sockhost;
This method returns a string which is the IPv4 or IPv6 address the
local socket is bound to. It returns "" when not connected.
sockport - TCP port of this end of the socket connection
$port = $obj->sockport;
This method returns the port number which the local socket is bound
to. It returns "" when not connected.
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 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 is 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
TELNETA ProtocolA Specification
http://tools.ietf.org/html/rfc854
RFC 1143
QA MethodA ofA ImplementingA TELNETA OptionA Negotiation
http://tools.ietf.org/html/rfc1143
TELNET Option Assignments
http://www.iana.org/assignments/telnet-options
EXAMPLES
Setting "prompt()" to match a user's shell prompt can be tricky. This
example logs in without knowing the shell prompt and then sets it to
match "prompt()". It requires /usr/bin/env and /bin/sh on the remote
host.
my $host = 'your_destination_host_here';
my $user = 'your_username_here';
my $passwd = 'your_password_here';
my ($t, @output);
## Create a Net::Telnet object.
use Net::Telnet ();
$t = new Net::Telnet (Timeout => 10);
## Connect and login.
$t->open($host);
$t->waitfor('/login: ?$/i');
$t->print($user);
$t->waitfor('/password: ?$/i');
$t->print($passwd);
## Switch to a known shell, using a known prompt.
$t->prompt('/<xPROMPTx> $/');
$t->errmode("return");
$t->cmd("exec /usr/bin/env 'PS1=<xPROMPTx> ' /bin/sh -i")
or die "login failed to remote host $host";
$t->errmode("die");
## Now you can do cmd() to your heart's content.
@output = $t->cmd("uname -a");
print @output;
exit;
Usually you want the remote TERM environment variable to be set to
something like "dumb" so you don't read escape sequences meant to be
interpreted by a display terminal. It is best to set it via "cmd()",
or via "waitfor()" and "print()". It is also possible to negotiate the
terminal type via telnet. Here is how to do that.
## Module import.
use Net::Telnet qw(TELNET_IAC TELNET_SB TELNET_SE TELOPT_TTYPE);
## Global variables.
my $Term;
## Main program.
{
my $host = "your_destination_host_here";
my $user = "your_username_here";
my $passwd = "your_password_here";
my $prompt = '/bash\$ $/'; # your regexp for shell prompt here
my $t;
$t = new Net::Telnet (Prompt => $prompt);
## Set up callbacks to negotiate terminal type.
$t->option_callback(sub {});
$t->suboption_callback(\&subopt_callback);
$t->option_accept(Do => TELOPT_TTYPE);
## Login and print value of TERM.
$Term = "dumb";
$t->open($host);
$t->login($user, $passwd);
print $t->cmd('hostname');
print "TERM=", $t->cmd('echo $TERM');
$t->close;
exit;
} # end main program
sub subopt_callback {
my ($t, $option, $parameters) = @_;
my $telcmd;
if ($option == TELOPT_TTYPE) {
$telcmd = pack("C4 A* C2", TELNET_IAC, TELNET_SB, TELOPT_TTYPE, 0,
$Term, TELNET_IAC, TELNET_SE);
$t->put(String => $telcmd,
Telnetmode => 0);
}
1;
} # end sub subopt_callback
You can also use Net::Telnet to interact with local programs. This
example changes a user's login password. It introduces the "spawn()"
subroutine to start a program and associate a filehandle with its
standard I/O. Because the passwd program always prompts for passwords
on its controlling terminal, the IO::Pty module is used to create a new
pseudo terminal for use by passwd. The Net::Telnet object reads and
writes to that pseudo terminal. To use the code below, substitute
"changeme" with the actual old and new passwords.
## Main program. {
my ($pty, $passwd);
my $oldpw = "changeme";
my $newpw = "changeme";
## Start passwd program.
$pty = spawn("passwd");
## 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.
$passwd->waitfor('/new (\w+\s)?password: ?$/i')
or die "bad old password: ", $passwd->lastline;
$passwd->print($newpw);
## Send new password verification.
$passwd->waitfor('/new (\w+\s)?password: ?$/i')
or die "bad new password: ", $passwd->lastline;
$passwd->print($newpw);
## Display success or failure.
$passwd->waitfor('/(changed|updated)/')
or die "bad new password: ", $passwd->lastline;
print $passwd->lastline;
$passwd->close;
exit;
} # end main program
sub spawn {
my (@cmd) = @_;
my ($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 its controlling terminal.
use POSIX ();
POSIX::setsid()
or die "setsid failed: $!";
## Associate process with a new controlling terminal.
$pty->make_slave_controlling_terminal;
$tty = $pty->slave;
$tty_fd = $tty->fileno;
close $pty;
## Make standard I/O use the new controlling terminal.
open STDIN, "<&$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 is an example that uses the openssh program to connect to a remote
host. It uses the "spawn()" subroutine, from the password changing
example above, to start the ssh program and then read and write to it
via a Net::Telnet object. This example turns off ssh host key
checking, which reduces your ability to know when someone on the
network is impersonating the remote host. To use the code below,
substitute "changeme" with the actual host, user, password, and command
prompt.
## Main program.
{
my $host = "changeme";
my $user = "changeme";
my $passwd = "changeme";
my $prompt = '/changeme\$ $/';
my ($buf, $match, $pty, $ssh, @lines);
## Start ssh program.
$pty = spawn("ssh",
"-l", $user,
"-e", "none",
"-F", "/dev/null",
"-o", "PreferredAuthentications=password",
"-o", "NumberOfPasswordPrompts=1",
"-o", "StrictHostKeyChecking=no",
"-o", "UserKnownHostsFile=/dev/null",
$host);
## 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,
-output_record_separator => "\r",
-cmd_remove_mode => 1);
## Wait for the password prompt and send password.
$ssh->waitfor(-match => '/password: ?$/i',
-errmode => "return")
or die "problem connecting to \"$host\": ", $ssh->lastline;
$ssh->print($passwd);
## Wait for the shell prompt.
(undef, $match) = $ssh->waitfor(-match => $ssh->prompt,
-match => '/^Permission denied/m',
-errmode => "return")
or return $ssh->error("login failed: expected shell prompt ",
"doesn't match actual\n");
return $ssh->error("login failed: bad login-name or password\n")
if $match =~ /^Permission denied/m;
## Run commands on remote host.
print $ssh->cmd("hostname");
print $ssh->cmd("uptime");
$ssh->close;
exit;
} # end main program
Some shells have a rather restrictive 255 character line limit. If you
run into this problem, here is an example for sending lines longer than
254 as a sequence of shorter lines.
## Main program.
{
my $host = "changeme";
my $user = "changeme";
my $passwd = "changeme";
my $prompt = '/changeme\$ $/';
my $cmd = join("", "echo ",
"11111111112222222222333333333344444444445555555555",
"66666666667777777777888888888899999999990000000000",
"11111111112222222222333333333344444444445555555555",
"66666666667777777777888888888899999999990000000000",
"11111111112222222222333333333344444444445555555555",
"66666666667777777777888888888899999999990000000000");
use Net::Telnet ();
my $t = new Net::Telnet (-prompt => $prompt);
$t->open($host);
$t->login($user, $passwd);
my @output = cmd_unixlong($t, $cmd);
print @output;
exit;
} # end main program
sub cmd_unixlong {
my ($obj, $cmd) = @_;
my ($line, $pos);
my $max_tty_line = 254;
## Start a Bourne shell.
$obj->cmd(-string => "/usr/bin/env " .
"'PS1=<xPROMPTx> ' 'PS2=<xPROMPTx> ' /bin/sh -i",
-prompt => '/<xPROMPTx> $/')
or return;
## Break-up the one large command line and send as shorter lines.
$pos = 0;
while (1) {
$line = substr $cmd, $pos, $max_tty_line;
$pos += length $line;
last unless $pos < length $cmd;
## Send the line with continuation char.
$obj->cmd(-string => "$line\\",
-prompt => '/<xPROMPTx> $/')
or return;
}
## Send the last line and return the output.
$obj->cmd("$line ; exit");
} # end sub cmd_unixlong
AUTHOR
Jay Rogers <jay@rgrs.com>
CREDITS
Dave Martin, Dave Cardosi
COPYRIGHT
Copyright 1997, 2000, 2002, 2013, 2021 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.
perl v5.30.3 2021-06-20 Net::Telnet(3)
net-telnet 3.50.0 - Generated Fri Jun 25 15:59:11 CDT 2021