Net::SSH::Expect(3) User Contributed Perl Documentation Net::SSH::Expect(3)NAMENet::SSH::Expect - SSH wrapper to execute remote commands
SYNOPSIS
use Net::SSH::Expect;
#
# You can do SSH authentication with user-password or without it.
#
# Making an ssh connection with user-password authentication
# 1) construct the object
my $ssh = Net::SSH::Expect->new (
host => "myserver.com",
password=> 'pass87word',
user => 'bnegrao',
raw_pty => 1
);
# 2) logon to the SSH server using those credentials.
# test the login output to make sure we had success
my $login_output = $ssh->login();
if ($login_output !~ /Welcome/) {
die "Login has failed. Login output was $login_output";
}
# - now you know you're logged in - #
# Starting ssh without password
# 1) run the constructor
my $ssh = Net::SSH::Expect->new (
host => "myserver.com",
user => 'bnegrao',
raw_pty => 1
);
# 2) now start the ssh process
$ssh->run_ssh() or die "SSH process couldn't start: $!";
# 3) you should be logged on now. Test if you received the remote prompt:
($ssh->read_all(2) =~ />\s*\z/) or die "where's the remote prompt?"
# - now you know you're logged in - #
# disable terminal translations and echo on the SSH server
# executing on the server the stty command:
$ssh->exec("stty raw -echo");
# runs arbitrary commands and print their outputs
# (including the remote prompt comming at the end)
my $ls = $ssh->exec("ls -l /");
print($ls);
my $who = $ssh->exec("who");
print ($who);
# When running a command that causes a huge output,
# lets get the output line by line:
$ssh->send("find /"); # using send() instead of exec()
my $line;
# returns the next line, removing it from the input stream:
while ( defined ($line = $ssh->read_line()) ) {
print $line . "\n";
}
# take a look in what is immediately available on the input stream
print $ssh->peek(0); # you'll probably see the remote prompt
# the last read_line() on the previous loop will not include the
# remote prompt that appears at the end of the output, because the prompt
# doesn't end with a '\n' character. So let's remove the remainder
# prompt from the input stream:
$ssh->eat($ssh->peek(0)); # removes whatever is on the input stream now
# We can also iterate over the output in chunks,
# printing everything that's available at each 1 second:
$ssh->send ("find /home");
my $chunk;
while ($chunk = $ssh->peek(1)) { # grabs chunks of output each 1 second
print $ssh->eat($chunk);
}
# Now let's run an interactive command, like passwd.
# This is done combining send() and waitfor() methods together:
$ssh->send("passwd");
$ssh->waitfor('password:\s*\z', 1) or die "prompt 'password' not found after 1 second";
$ssh->send("curren_password");
$ssh->waitfor(':\s*\z', 1) or die "prompt 'New password:' not found";
$ssh->send("new_password");
$ssh->waitfor(':\s*\z', 1) or die "prompt 'Confirm new password:' not found";
$ssh->send("new_password");
# check that we have the system prompt again.
my ($before_match, $match) = $ssh->waitfor('>\s*\z', 1); # waitfor() in a list context
die "passwd failed. passwd said '$before_match'." unless ($match);
# closes the ssh connection
$ssh->close();
DESCRIPTION
This module is a wrapper to the ssh executable that is available in
your system's $PATH. Use this module to execute commands on the remote
SSH server. It authenticates with the user and password you passed in
the constructor's attributes "user" and "password".
Once an ssh connection was started using the "connect()" method it will
remain open until you call the "close()" method. This allows you
execute as many commands as you want with the "exec()" method using
only one connection. This is a better approach over other ssh wrapper
implementations, i.e: Net::SCP, Net::SSH and Net::SCP::Expect, that
start a new ssh connection each time a remote command is issued or a
file is transfered.
It uses Expect.pm module to interact with the SSH server. A
"get_expect()" method is provided so you can obtain the internal
"Expect" object connected to the SSH server. Use this only if you have
some special need that you can't do with the "exec()" method.
This module was inspired by Net::SCP::Expect
http://search.cpan.org/~djberg/Net-SCP-Expect-0.12/Expect.pm
<http://search.cpan.org/~djberg/Net-SCP-Expect-0.12/Expect.pm> and by
Net::Telnet and some of its methods work the same as these two modules.
IMPORTANT NOTES ABOUT DEALING WITH SSH AND PSEUDO-TERMINALS
This module uses Expect to start the local ssh client process, and
Expect will interact with this process through a local pseudo-terminal
(ptty). Similarly, the ssh client will connect to the SSH server and
there will receive an ssh login process attached to a ptty too.
During my tests I realized that the I/O to and from the ssh server
changes drastically from OS to OS if we let the local and remote pttys
configured on their defaults. The echo's and the \r\n translations make
a mess that we are never sure what will be sent to the other side and
what will be received here.
Many ptty features are system dependent and we can't rely on them
working the same on different OS's.
To avoid these problems I always recommend you to:
1) enable the 'raw_pty' constructor attribute. This disables most (if
not all) of the problematic features on the local ptty.
2) Similarly set the ptty on the remote server to 'raw -echo' as soon
as you login. This can be done with:
$ssh->exec("stty raw -echo");
Obviously your server must support the 'stty' command for that.
3) If you won't run on the server interactive commands that prompt for
input, like 'passwd', you could prevent the ssh server from attributing
a ptty for the ssh login process. This is done by enabling the
'no_terminal' constructor attribute. What that does is passing the '-T'
option to the ssh client process when it is created. From the BSD ssh
client manual:
-T Disable pseudo-tty allocation.
This will create the cleaner connection possible. You won't have a ptty
on the server, and, weirdly, you won't receive a remote prompt. Try
yourself 'ssh -T my.ssh.server' to see how it works. Notice that some
system commands that rely on a terminal won't work, say, 'who am i',
'stty', etc.
Also, interactive commands like 'passwd' or 'mail' won't be able to
print their prompts.
But other system commands will run better: 'ls -l' will be printed
without terminal control characters. 'ps -ef' will have the command
lines printed fully, since there is no 'columns' terminal limitation.
Moral of the story: pseudo terminals do many character translations
that can bring some unexpected results in some situations. Avoid them
if you can.
EXPORT
None by default.
CONSTRUCTOR ATTRIBUTES
The constructor accepts all the following attributes that can be set in
the form of attribute => 'value' pairs. They are presentend in three
groups: 1) attributes to configure the ssh client process; 2)
attributes to configure the underlying Expect object; 3) attributes to
configure this module;
ATTRIBUTES TO CONFIGURE THE SSH CLIENT PROCESS
Some of the attributes bellow will enable/disable some options of the
ssh client. Refer to you ssh client documentation to know what each one
does.
string binary
the complete path to the 'ssh' executable in your machine. The
default is 'ssh' what means the ssh used by default is the first
one found in your $PATH environment variable.
string user
the username to login.
string password
the password used to login. You won't need to set this field if you
have public-key authentication configured for you ssh user. Read
run_ssh() documentation for more info.
string host
the address(dns name/ip) to the ssh server
string port
Feeds the -p ssh client option with alternate ssh port. This option
is not set by default.
boolean no_terminal
If enabled adds the -T ssh client option to the ssh command line.
See the discussion on "IMPORTANT NOTES ABOUT DEALING WITH SSH AND
PSEUDO-TERMINALS" to know if you want to enable this.
char escape_char
Passes a character to the -e ssh client option. This enables ssh
escapes. Since this option can cause trouble, it is explicitly
turned off by default with a '-e none' option being set on the ssh
command line.
string ssh_option
This lets you add your own ssh options to the command line. Set
this string to the options you want, like '-v -p 2022', and your
options will be added to the ssh command line that will start the
ssh process.
CONSTRUCTOR OPTIONS THAT CONFIGURE THE INTERNAL EXPECT OBJECT
The following constructor attributes can be used to configure special
features of the internal Expect object used to communicate with the ssh
server. These options will be passed to the Expect object inside the
"connect" method before it spawns the ssh process.
string log_file
Used as argument to the internal Expect->log_file() method. Default
is no logfile.
boolean log_stdout
Used as argument to the internal Expect->log_sdtout() method.
Default is 0, to disable log to stdout.
boolean exp_internal
Argument to be passed to the internal Expect->exp_internal()
method. Default is 0, to disable the internal exposure.
boolean exp_debug
Argument to be passed to the internal Expect->debug() method.
Default is 0, to disable debug.
boolean raw_pty
Argument to be passed to the internal Expect->raw_pty() method.
It's recommended that you enable this. See the disscussion in
"IMPORTANT NOTES ABOUT DEALING WITH SSH AND PSEUDO-TERMINALS" to
know why. Default is 0 to let the local ptty as its defaults.
boolean restart_timeout_upon_receive
If this is enabled the timeout in all reading operations works as
an inactivity timeout - it'll not start counting while there is
data arriving on input stream. Default is 0.
CONSTRUCTOR OPTIONS TO CONFIGURE THIS MODULE
string terminator
the line terminator in use on the SSH server, this will added at
the end of each command passed to the "exec()" method. The default
is "\n".
It also affects the read_line() method, it expect each line to be
terminated by the 'teminator' character. Lines can also be ended
with "\r" or "\r\n" in some systems. Remember to adjust this for
your system.
You can also use the terminator() method to set this attribute.
integer timeout
The maximum time to wait for a pattern to show up on input stream
before giving up in a read operation. The default is 1 second.
Timeout must always be an integer >= 0.
This attribute can also be get/set with the "timeout()" method.
boolean debug
Causes some methods to print debug messages to the STDERR. This
feature is not widely implemented yet. (only eat() implements it
until this moment)
METHODS
boolean run_ssh() - forks the ssh client process
# boolean run_ssh() - forks the ssh client process opening an ssh connection to the SSH server.
#
# This method has three roles:
# 1) Instantiate a new Expect object configuring it with all the defaults and user-defined
# settings.
# 2) Define the ssh command line using the defaults and user-defined settings
# 3) Fork the ssh process using the spawn() method of the Expect instance we created.
# The SSH connection is established on this step using the user account set in the 'user'
# constructor attribute. No password is sent here, that happens only in the login() method.
#
# This method is run internally by the login() method so you don't need to run it yourself
# in most of the cases. You'll run this method alone if you had set up public-key authentication
# between the ssh client and the ssh server. In this case you only need to call this method
# to have an authenticated ssh connection, you won't call login(). Note that when you
# use public-key authentication you won't need to set the 'password' constructor attribute
# but you still need to define the 'user' attribute.
# If you don't know how to setup public-key authentication there's a good guide at
# http://sial.org/howto/openssh/publickey-auth/
#
# returns:
# boolean: 1 if the ssh ran OK or 0 otherwise. In case of failures, use $! to do get info.
string login([$login_prompt, $password_prompt] [,$test_success]) -
authenticates on the ssh server.
# string login ([$login_prompt, $password_prompt] [,$test_success]) - authenticates on the ssh server.
# This method responds to the authentication prompt sent by the SSH server.
# You can customize the "Login:" and "Password:" prompts that must be expected by passing their
# patterns as arguments to this method, although this method has default values that work to most
# SSH servers out there.
# It runs the run_ssh() method only if it wasn't run before(), but it'll die
# if run_ssh() returns false.
#
# param:
# $login_prompt: A pattern string used to match the "Login:" prompt. The default
# pattern is qr/ogin:\s*$/
#
# $password_prompt: A pattern string used to match the "Password:" prompt. The default
# pattern is qr/[Pp]assword.*?:|[Pp]assphrase.*?:/
#
# $test_success: 0 | 1. if 1, login will do an extra-test to verify if the password
# entered was accepted. The test consists in verifying if, after sending the password,
# the "Password" prompt shows up again what would indicate that the password was rejected.
# This test is disabled by default.
#
# OBS: the number of paramaters passed to this method will tell it what parameters are being passed:
# 0 parameters: login() : All the default values will be used.
# 1 parameter: login(1) : The $test_success parameter is set.
# 2 parameters: login("Login:", "Password:") : the $login_prompt and $password_prompt parameters are set.
# 3 parameters: login("Login:", "Password;", 1) : the three parameters received values on this order.
#
# returns:
# string: whatever the SSH server wrote in my input stream after loging in. This usually is some
# welcome message and/or the remote prompt. You could use this string to do your verification
# that the login was successful. The content returned is removed from the input stream.
# dies:
# IllegalState: if any of 'host' or 'user' or 'password' fields are unset.
# SSHProccessError: if run_ssh() failed to spawn the ssh process
# SSHConnectionError: if the connection failed for some reason, like invalid 'host' address or network problems.
string exec($cmd [,$timeout]) - executes a command in the remote
machine returning its output
exec('command') runs 'command' in the remote machine and returns
all the output generated by 'command' into a string.
boolean waitfor($pattern [,$timeout])
# boolean waitfor ($string [, $timeout, $match_type])
# This method reads until a pattern or string is found in the input stream.
# All the characters before and including the match are removed from the input stream.
#
# After waitfor returns, use the methods before(), match() and after() to get the data
# 'before the match', 'what matched', and 'after the match' respectively.
#
# If waitfor returns false, whatever content is on input stream can be accessed with
# before(). In this case before() will return the same content as peek().
#
# params:
# $string: a string to be matched. It can be a regular expression or a literal string
# anb its interpretation as one or other depends on $match_type. Default is
# 're', what treats $string as a regular expression.
#
# $timeout: the timeout in seconds while waiting for $string
#
# $match_type: match_type affects how $string will be matched:
# '-re': means $string is a regular expression.
# '-ex': means $string is an "exact match", i.e., will be matched literally.
#
# returns:
# boolean: 1 is returned if string was found, 0 otherwise. When the match fails
# waitfor() will only return after waiting $timeout seconds.
#
# dies:
# SSH_CONNECTION_ABORTED if EOF is found (error type 2)
# SSH_PROCESS_ERROR if the ssh process has died (error type 3)
# SSH_CONNECTION_ERROR if unknown error (type 4) is found
string before() - returns the "before match" data of the last waitfor()
call.
When waitfor() matches, if there is any content before the match,
this will be returned by before().
If the last waitfor() didn't match, before() will return all the
current content on the input stream, just as if you had called
peek() with the same timeout.
string match() - returns the "match" data of the last waitfor() call,
or undef if didn't match.
string after() - returns the "after match" data of the last waitfor()
call, or undef if didn't match.
void close() - terminates the ssh connection
void send($string) - sends $string to the SSH server, returns nothing
Sends the string to the SSH server. If the ssh server process is
attached to a pseudo-terminal (this is the default) it is likely
that the echo terminal property will be on, what will make the
server place the command you just sent in our input stream, i.e.,
you'll see the command you sent in your next read operation.
To avoid this, try to disable the echo property on the server-side,
using
$ssh->exec("stty -echo");
It's also advisable to disable the terminal character convertions
on server-side, what will make you sure that every character you
sent will be received "as-is" to the other side.
So you'll probably use this to disable character conversions and
echo:
$ssh->exec("stty raw -echo");
Of course you're server must support the 'stty' command for that
work.
To guarantee that your characters are not converted by your local
pseudo-terminal before you send them out, set the constructor
option:
raw_pty => 1
And if you don't need a terminal on the server-side at all, set the
constructor option bellow to 1:
no_terminal => 1
string peek([$timeout]) - returns what is in the input stream without
removing anything
# peek([$timeout]) - returns what is in the input stream without removing anything
# peek() returns what is available on the input stream until $timeout seconds.
# If there is data continuosly arriving on the input stream, subsequent calls to peek()
# will return a growing amount of data.
#
# dies:
# SSH_CONNECTION_ABORTED if EOF is found (error type 2)
# SSH_PROCESS_ERROR if the ssh process has died (error type 3)
# SSH_CONNECTION_ERROR if unknown error (type 4) is found
string eat($string) - removes all the head of the input stream until
$string inclusive.
# string eat($string)- removes all the head of the input stream until $string inclusive.
# eat() will only be able to remove the $string if it's currently present on the
# input stream because eat() will wait 0 seconds before removing it.
#
# Use it associated with peek to eat everything that appears on the input stream:
#
# while ($chunk = $exp->eat($exp->peak())) {
# print $chunk;
# }
#
# Or use the read_all() method that does the above loop for you returning the accumulated
# result.
#
# param:
# string: a string currently available on the input stream.
# If $string doesn't start in the head, all the content before $string will also
# be removed.
#
# If $string is undef or empty string it will be returned immediately as it.
#
# returns:
# string: the removed content or empty string if there is nothing in the input stream.
#
# dies:
# SSH_CONNECTION_ABORTED if EOF is found (error type 2)
# SSH_PROCESS_ERROR if the ssh process has died (error type 3)
# SSH_CONNECTION_ERROR if unknown error (type 4) is found
#
# debbuging features:
# The following warnings are printed to STDERR if $exp->debug() == 1:
# eat() prints a warning is $string wasn't found in the head of the input stream.
# eat() prints a warning is $string was empty or undefined.
#
string read_all([$timeout]) - reads and removes all the output from the
input stream.
The reading/removing process will be interrupted after $timeout
seconds of inactivity on the input stream.
string read_line([$timeout]) - reads the next line from the input
stream and returns it.
# string read_line([$timeout]) - reads the next line from the input stream
# Read a line of text. A line is considered to be terminated by the 'teminator'
# character. Default is "\n". Lines can also be ended with "\r" or "\r\n".
# Remember to adequate this for your system with the terminator() method.
# When there are no more lines available, read_line() returns undef. Note that this doen't mean
# there is no data left on input stream since there can be a string not terminated with the
# 'terminator' character, notably the remote prompt could be left there when read_line() returns
# undef.
#
# params:
# $timeout: the timeout waiting for a line. Defaults to timeout().
#
# returns:
# string: a line on the input stream, without the trailing 'terminator' character.
# An empty string indicates that the line read only contained the 'terminator'
# character (an empty line).
# undef: when there are no more lines on the input stream.
#
void restart_timeout_upon_receive( 0 | 1 ) - changes the timeout
counter behaviour
# void restart_timeout_upon_receive( 0 | 1 ) - changes the timeout counter behaviour
# params:
# boolean: if true, sets the timeout to "inactivity timeout", if false
# sets it to "absolute timeout".
# dies:
# IllegalParamenter if argument is not given.
Expect get_expect() - returns the internal Expect object
params:
none
returns:
an "Expect" object connected to the SSH server. It will die if
you try to run it without being connected.
dies:
IllegalState: if this there is no valid ssh connection
established
SEE ALSO
Net::SCP::Expect, Net::SCP, Net::SSH::Perl, Expect
REPORTING BUGS
To report bugs please use the bug reporting tool available on CPAN
website, in the module's page. That way I can keep track of what I need
to do and I can also communicate with you through that tool.
AUTHOR
Bruno Negrao Guimaraes Zica. <bnegrao@cpan.org>.
THANKS
Daniel Berger, author of Net::SCP::Expect. Special thanks to the people
helping me improve this module by reporting their tests and the bugs
they find.
COPYRIGHT AND LICENSE
Copyright (C) 2007 by Bruno Negrao Guimaraes Zica
This library is free software; you can redistribute it and/or modify it
under the same terms as Perl itself, either Perl version 5.8.3 or, at
your option, any later version of Perl 5 you may have available.
perl v5.14.1 2008-04-23 Net::SSH::Expect(3)
