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Expect(3pm) User Contributed Perl Documentation Expect(3pm)
NAME
Expect.pm - Expect for Perl
VERSION
1.21
SYNOPSIS
use Expect;
# create an Expect object by spawning another process
my $exp = Expect->spawn($command, @params)
or die "Cannot spawn $command: $!\n";
# or by using an already opened filehandle (e.g. from Net::Telnet)
my $exp = Expect->exp_init(\*FILEHANDLE);
# if you prefer the OO mindset:
my $exp = new Expect;
$exp->raw_pty(1);
$exp->spawn($command, @parameters)
or die "Cannot spawn $command: $!\n";
# send some string there:
$exp->send("string\n");
# or, for the filehandle mindset:
print $exp "string\n";
# then do some pattern matching with either the simple interface
$patidx = $exp->expect($timeout, @match_patterns);
# or multi-match on several spawned commands with callbacks,
# just like the Tcl version
$exp->expect($timeout,
[ qr/regex1/ => sub { my $exp = shift;
$exp->send("response\n");
exp_continue; } ],
[ "regexp2" , \&callback, @cbparms ],
);
# if no longer needed, do a soft_close to nicely shut down the command
$exp->soft_close();
# or be less patient with
$exp->hard_close();
Expect.pm is built to either spawn a process or take an existing filehandle and interact
with it such that normally interactive tasks can be done without operator assistance. This
concept makes more sense if you are already familiar with the versatile Tcl version of
Expect. The public functions that make up Expect.pm are:
Expect->new()
Expect::interconnect(@objects_to_be_read_from)
Expect::test_handles($timeout, @objects_to_test)
Expect::version($version_requested | undef);
$object->spawn(@command)
$object->clear_accum()
$object->set_accum($value)
$object->debug($debug_level)
$object->exp_internal(0 | 1)
$object->notransfer(0 | 1)
$object->raw_pty(0 | 1)
$object->stty(@stty_modes) # See the IO::Stty docs
$object->slave()
$object->before();
$object->match();
$object->after();
$object->matchlist();
$object->match_number();
$object->error();
$object->command();
$object->exitstatus();
$object->pty_handle();
$object->do_soft_close();
$object->restart_timeout_upon_receive(0 | 1);
$object->interact($other_object, $escape_sequence)
$object->log_group(0 | 1 | undef)
$object->log_user(0 | 1 | undef)
$object->log_file("filename" | $filehandle | \&coderef | undef)
$object->manual_stty(0 | 1 | undef)
$object->match_max($max_buffersize or undef)
$object->pid();
$object->send_slow($delay, @strings_to_send)
$object->set_group(@listen_group_objects | undef)
$object->set_seq($sequence,\&function,\@parameters);
There are several configurable package variables that affect the behavior of Expect. They
are:
$Expect::Debug;
$Expect::Exp_Internal;
$Expect::IgnoreEintr;
$Expect::Log_Group;
$Expect::Log_Stdout;
$Expect::Manual_Stty;
$Expect::Multiline_Matching;
$Expect::Do_Soft_Close;
DESCRIPTION
The Expect module is a successor of Comm.pl and a descendent of Chat.pl. It more closely
ressembles the Tcl Expect language than its predecessors. It does not contain any of the
networking code found in Comm.pl. I suspect this would be obsolete anyway given the advent
of IO::Socket and external tools such as netcat.
Expect.pm is an attempt to have more of a switch() & case feeling to make decision
processing more fluid. Three separate types of debugging have been implemented to make
code production easier.
It is possible to interconnect multiple file handles (and processes) much like Tcl's
Expect. An attempt was made to enable all the features of Tcl's Expect without forcing Tcl
on the victim programmer :-) .
Please, before you consider using Expect, read the FAQs about "I want to automate password
entry for su/ssh/scp/rsh/..." and "I want to use Expect to automate [anything with a
buzzword]..."
USAGE
new Expect ()
Creates a new Expect object, i.e. a pty. You can change parameters on it before
actually spawning a command. This is important if you want to modify the terminal
settings for the slave. See slave() below. The object returned is actually a
reblessed IO::Pty filehandle, so see there for additional methods.
Expect->exp_init(\*FILEHANDLE) or
Expect->init(\*FILEHANDLE)
Initializes $new_handle_object for use with other Expect functions. It must be passed
a _reference_ to FILEHANDLE if you want it to work properly. IO::File objects are
preferable. Returns a reference to the newly created object.
You can use only real filehandles, certain tied filehandles (e.g. Net::SSH2) that lack
a fileno() will not work. Net::Telnet objects can be used but have been reported to
work only for certain hosts. YMMV.
Expect->spawn($command, @parameters) or
$object->spawn($command, @parameters) or
new Expect ($command, @parameters)
Forks and execs $command. Returns an Expect object upon success or "undef" if the fork
was unsuccessful or the command could not be found. spawn() passes its parameters
unchanged to Perls exec(), so look there for detailed semantics.
Note that if spawn cannot exec() the given command, the Expect object is still valid
and the next expect() will see "Cannot exec", so you can use that for error handling.
Also note that you cannot reuse an object with an already spawned command, even if
that command has exited. Sorry, but you have to allocate a new object...
$object->debug(0 | 1 | 2 | 3 | undef)
Sets debug level for $object. 1 refers to general debugging information, 2 refers to
verbose debugging and 0 refers to no debugging. If you call debug() with no parameters
it will return the current debugging level. When the object is created the debugging
level will match that $Expect::Debug, normally 0.
The '3' setting is new with 1.05, and adds the additional functionality of having the
_full_ accumulated buffer printed every time data is read from an Expect object. This
was implemented by request. I recommend against using this unless you think you need
it as it can create quite a quantity of output under some circumstances..
$object->exp_internal(1 | 0)
Sets/unsets 'exp_internal' debugging. This is similar in nature to its Tcl
counterpart. It is extremely valuable when debugging expect() sequences. When the
object is created the exp_internal setting will match the value of
$Expect::Exp_Internal, normally 0. Returns the current setting if called without
parameters. It is highly recommended that you make use of the debugging features lest
you have angry code.
$object->raw_pty(1 | 0)
Set pty to raw mode before spawning. This disables echoing, CR->LF translation and an
ugly hack for broken Solaris TTYs (which send <space><backspace> to slow things down)
and thus gives a more pipe-like behaviour (which is important if you want to transfer
binary content). Note that this must be set before spawning the program.
$object->stty(qw(mode1 mode2...))
Sets the tty mode for $object's associated terminal to the given modes. Note that on
many systems the master side of the pty is not a tty, so you have to modify the slave
pty instead, see next item. This needs IO::Stty installed, which is no longer
required.
$object->slave()
Returns a filehandle to the slave part of the pty. Very useful in modifying the
terminal settings:
$object->slave->stty(qw(raw -echo));
Typical values are 'sane', 'raw', and 'raw -echo'. Note that I recommend setting the
terminal to 'raw' or 'raw -echo', as this avoids a lot of hassle and gives pipe-like
(i.e. transparent) behaviour (without the buffering issue).
$object->print(@strings) or
$object->send(@strings)
Sends the given strings to the spawned command. Note that the strings are not logged
in the logfile (see print_log_file) but will probably be echoed back by the pty,
depending on pty settings (default is echo) and thus end up there anyway. This must
also be taken into account when expect()ing for an answer: the next string will be the
command just sent. I suggest setting the pty to raw, which disables echo and makes
the pty transparently act like a bidirectional pipe.
$object->expect($timeout, @match_patterns)
or, more like Tcl/Expect,
expect($timeout,
'-i', [ $obj1, $obj2, ... ],
[ $re_pattern, sub { ...; exp_continue; }, @subparms, ],
[ 'eof', sub { ... } ],
[ 'timeout', sub { ... }, \$subparm1 ],
'-i', [ $objn, ...],
'-ex', $exact_pattern, sub { ... },
$exact_pattern, sub { ...; exp_continue_timeout; },
'-re', $re_pattern, sub { ... },
'-i', \@object_list, @pattern_list,
...);
Simple interface:
Given $timeout in seconds Expect will wait for $object's handle to produce one of the
match_patterns, which are matched exactly by default. If you want a regexp match,
prefix the pattern with '-re'.
Due to o/s limitations $timeout should be a round number. If $timeout is 0 Expect will
check one time to see if $object's handle contains any of the match_patterns. If
$timeout is undef Expect will wait forever for a pattern to match.
If called in a scalar context, expect() will return the position of the matched
pattern within $match_patterns, or undef if no pattern was matched. This is a position
starting from 1, so if you want to know which of an array of @matched_patterns matched
you should subtract one from the return value.
If called in an array context expect() will return ($matched_pattern_position, $error,
$successfully_matching_string, $before_match, and $after_match).
$matched_pattern_position will contain the value that would have been returned if
expect() had been called in a scalar context. $error is the error that occurred that
caused expect() to return. $error will contain a number followed by a string
equivalent expressing the nature of the error. Possible values are undef, indicating
no error, '1:TIMEOUT' indicating that $timeout seconds had elapsed without a match,
'2:EOF' indicating an eof was read from $object, '3: spawn id($fileno) died'
indicating that the process exited before matching and '4:$!' indicating whatever
error was set in $ERRNO during the last read on $object's handle or during select().
All handles indicated by set_group plus STDOUT will have all data to come out of
$object printed to them during expect() if log_group and log_stdout are set.
Changed from older versions is the regular expression handling. By default now all
strings passed to expect() are treated as literals. To match a regular expression pass
'-re' as a parameter in front of the pattern you want to match as a regexp.
Example:
$object->expect(15, 'match me exactly','-re','match\s+me\s+exactly');
This change makes it possible to match literals and regular expressions in the same
expect() call.
Also new is multiline matching. ^ will now match the beginning of lines.
Unfortunately, because perl doesn't use $/ in determining where lines break using $ to
find the end of a line frequently doesn't work. This is because your terminal is
returning "\r\n" at the end of every line. One way to check for a pattern at the end
of a line would be to use \r?$ instead of $.
Example: Spawning telnet to a host, you might look for the escape character. telnet
would return to you "\r\nEscape character is '^]'.\r\n". To find this you might use
$match='^Escape char.*\.\r?$';
$telnet->expect(10,'-re',$match);
New more Tcl/Expect-like interface:
It's now possible to expect on more than one connection at a time by specifying '"-i"'
and a single Expect object or a ref to an array containing Expect objects, e.g.
expect($timeout,
'-i', $exp1, @patterns_1,
'-i', [ $exp2, $exp3 ], @patterns_2_3,
)
Furthermore, patterns can now be specified as array refs containing [$regexp, sub {
...}, @optional_subprams] . When the pattern matches, the subroutine is called with
parameters ($matched_expect_obj, @optional_subparms). The subroutine can return the
symbol `exp_continue' to continue the expect matching with timeout starting anew or
return the symbol `exp_continue_timeout' for continuing expect without resetting the
timeout count.
$exp->expect($timeout,
[ qr/username: /i, sub { my $self = shift;
$self->send("$username\n");
exp_continue; }],
[ qr/password: /i, sub { my $self = shift;
$self->send("$password\n");
exp_continue; }],
$shell_prompt);
`expect' is now exported by default.
$object->exp_before() or
$object->before()
before() returns the 'before' part of the last expect() call. If the last expect()
call didn't match anything, exp_before() will return the entire output of the object
accumulated before the expect() call finished.
Note that this is something different than Tcl Expects before()!!
$object->exp_after() or
$object->after()
returns the 'after' part of the last expect() call. If the last expect() call didn't
match anything, exp_after() will return undef().
$object->exp_match() or
$object->match()
returns the string matched by the last expect() call, undef if no string was matched.
$object->exp_match_number() or
$object->match_number()
exp_match_number() returns the number of the pattern matched by the last expect()
call. Keep in mind that the first pattern in a list of patterns is 1, not 0. Returns
undef if no pattern was matched.
$object->exp_matchlist() or
$object->matchlist()
exp_matchlist() returns a list of matched substrings from the brackets () inside the
regexp that last matched. ($object->matchlist)[0] thus corresponds to $1,
($object->matchlist)[1] to $2, etc.
$object->exp_error() or
$object->error()
exp_error() returns the error generated by the last expect() call if no pattern was
matched. It is typically useful to examine the value returned by before() to find out
what the output of the object was in determining why it didn't match any of the
patterns.
$object->clear_accum()
Clear the contents of the accumulator for $object. This gets rid of any residual
contents of a handle after expect() or send_slow() such that the next expect() call
will only see new data from $object. The contents of the accumulator are returned.
$object->set_accum($value)
Sets the content of the accumulator for $object to $value. The previous content of the
accumulator is returned.
$object->exp_command() or
$object->command()
exp_command() returns the string that was used to spawn the command. Helpful for
debugging and for reused patternmatch subroutines.
$object->exp_exitstatus() or
$object->exitstatus()
Returns the exit status of $object (if it already exited).
$object->exp_pty_handle() or
$object->pty_handle()
Returns a string representation of the attached pty, for example: `spawn id(5)' (pty
has fileno 5), `handle id(7)' (pty was initialized from fileno 7) or `STDIN'. Useful
for debugging.
$object->restart_timeout_upon_receive(0 | 1)
If this is set to 1, the expect timeout is retriggered whenever something is received
from the spawned command. This allows to perform some aliveness testing and still
expect for patterns.
$exp->restart_timeout_upon_receive(1);
$exp->expect($timeout,
[ timeout => \&report_timeout ],
[ qr/pattern/ => \&handle_pattern],
);
Now the timeout isn't triggered if the command produces any kind of output, i.e. is
still alive, but you can act upon patterns in the output.
$object->notransfer(1 | 0)
Do not truncate the content of the accumulator after a match. Normally, the
accumulator is set to the remains that come after the matched string. Note that this
setting is per object and not per pattern, so if you want to have normal acting
patterns that truncate the accumulator, you have to add a
$exp->set_accum($exp->after);
to their callback, e.g.
$exp->notransfer(1);
$exp->expect($timeout,
# accumulator not truncated, pattern1 will match again
[ "pattern1" => sub { my $self = shift;
...
} ],
# accumulator truncated, pattern2 will not match again
[ "pattern2" => sub { my $self = shift;
...
$self->set_accum($self->after());
} ],
);
This is only a temporary fix until I can rewrite the pattern matching part so it can
take that additional -notransfer argument.
Expect::interconnect(@objects);
Read from @objects and print to their @listen_groups until an escape sequence is
matched from one of @objects and the associated function returns 0 or undef. The
special escape sequence 'EOF' is matched when an object's handle returns an end of
file. Note that it is not necessary to include objects that only accept data in
@objects since the escape sequence is _read_ from an object. Further note that the
listen_group for a write-only object is always empty. Why would you want to have
objects listening to STDOUT (for example)? By default every member of @objects _as
well as every member of its listen group_ will be set to 'raw -echo' for the duration
of interconnection. Setting $object->manual_stty() will stop this behavior per
object. The original tty settings will be restored as interconnect exits.
For a generic way to interconnect processes, take a look at IPC::Run.
Expect::test_handles($timeout, @objects)
Given a set of objects determines which objects' handles have data ready to be read.
Returns an array who's members are positions in @objects that have ready handles.
Returns undef if there are no such handles ready.
Expect::version($version_requested or undef);
Returns current version of Expect. As of .99 earlier versions are not supported. Too
many things were changed to make versioning possible.
$object->interact( "\*FILEHANDLE, $escape_sequence")
interact() is essentially a macro for calling interconnect() for connecting 2
processes together. \*FILEHANDLE defaults to \*STDIN and $escape_sequence defaults to
undef. Interaction ceases when $escape_sequence is read from FILEHANDLE, not $object.
$object's listen group will consist solely of \*FILEHANDLE for the duration of the
interaction. \*FILEHANDLE will not be echoed on STDOUT.
$object->log_group(0 | 1 | undef)
Set/unset logging of $object to its 'listen group'. If set all objects in the listen
group will have output from $object printed to them during $object->expect(),
$object->send_slow(), and "Expect::interconnect($object , ...)". Default value is on.
During creation of $object the setting will match the value of $Expect::Log_Group,
normally 1.
$object->log_user(0 | 1 | undef) or
$object->log_stdout(0 | 1 | undef)
Set/unset logging of object's handle to STDOUT. This corresponds to Tcl's log_user
variable. Returns current setting if called without parameters. Default setting is
off for initialized handles. When a process object is created (not a filehandle
initialized with exp_init) the log_stdout setting will match the value of
$Expect::Log_Stdout variable, normally 1. If/when you initialize STDIN it is usually
associated with a tty which will by default echo to STDOUT anyway, so be careful or
you will have multiple echoes.
$object->log_file("filename" | $filehandle | \&coderef | undef)
Log session to a file. All characters send to or received from the spawned process
are written to the file. Normally appends to the logfile, but you can pass an
additional mode of "w" to truncate the file upon open():
$object->log_file("filename", "w");
Returns the logfilehandle.
If called with an undef value, stops logging and closes logfile:
$object->log_file(undef);
If called without argument, returns the logfilehandle:
$fh = $object->log_file();
Can be set to a code ref, which will be called instead of printing to the logfile:
$object->log_file(\&myloggerfunc);
$object->print_log_file(@strings)
Prints to logfile (if opened) or calls the logfile hook function. This allows the
user to add arbitraty text to the logfile. Note that this could also be done as
$object->log_file->print() but would only work for log files, not code hooks.
$object->set_seq($sequence, \&function, \@function_parameters)
During Expect->interconnect() if $sequence is read from $object &function will be
executed with parameters @function_parameters. It is _highly recommended_ that the
escape sequence be a single character since the likelihood is great that the sequence
will be broken into to separate reads from the $object's handle, making it impossible
to strip $sequence from getting printed to $object's listen group. \&function should
be something like 'main::control_w_function' and @function_parameters should be an
array defined by the caller, passed by reference to set_seq(). Your function should
return a non-zero value if execution of interconnect() is to resume after the function
returns, zero or undefined if interconnect() should return after your function
returns. The special sequence 'EOF' matches the end of file being reached by $object.
See interconnect() for details.
$object->set_group(@listener_objects)
@listener_objects is the list of objects that should have their handles printed to by
$object when Expect::interconnect, $object->expect() or $object->send_slow() are
called. Calling w/out parameters will return the current list of the listener objects.
$object->manual_stty(0 | 1 | undef)
Sets/unsets whether or not Expect should make reasonable guesses as to when and how to
set tty parameters for $object. Will match $Expect::Manual_Stty value (normally 0)
when $object is created. If called without parameters manual_stty() will return the
current manual_stty setting.
$object->match_max($maximum_buffer_length | undef) or
$object->max_accum($maximum_buffer_length | undef)
Set the maximum accumulator size for object. This is useful if you think that the
accumulator will grow out of hand during expect() calls. Since the buffer will be
matched by every match_pattern it may get slow if the buffer gets too large. Returns
current value if called without parameters. Not defined by default.
$object->notransfer(0 | 1)
If set, matched strings will not be deleted from the accumulator. Returns current
value if called without parameters. False by default.
$object->exp_pid() or
$object->pid()
Return pid of $object, if one exists. Initialized filehandles will not have pids (of
course).
$object->send_slow($delay, @strings);
print each character from each string of @strings one at a time with $delay seconds
before each character. This is handy for devices such as modems that can be annoying
if you send them data too fast. After each character $object will be checked to
determine whether or not it has any new data ready and if so update the accumulator
for future expect() calls and print the output to STDOUT and @listen_group if
log_stdout and log_group are appropriately set.
Configurable Package Variables:
$Expect::Debug
Defaults to 0. Newly created objects have a $object->debug() value of $Expect::Debug.
See $object->debug();
$Expect::Do_Soft_Close
Defaults to 0. When destroying objects, soft_close may take up to half a minute to
shut everything down. From now on, only hard_close will be called, which is less
polite but still gives the process a chance to terminate properly. Set this to '1'
for old behaviour.
$Expect::Exp_Internal
Defaults to 0. Newly created objects have a $object->exp_internal() value of
$Expect::Exp_Internal. See $object->exp_internal().
$Expect::IgnoreEintr
Defaults to 0. If set to 1, when waiting for new data, Expect will ignore EINTR errors
and restart the select() call instead.
$Expect::Log_Group
Defaults to 1. Newly created objects have a $object->log_group() value of
$Expect::Log_Group. See $object->log_group().
$Expect::Log_Stdout
Defaults to 1 for spawned commands, 0 for file handles attached with exp_init(). Newly
created objects have a $object->log_stdout() value of $Expect::Log_Stdout. See
$object->log_stdout().
$Expect::Manual_Stty
Defaults to 0. Newly created objects have a $object->manual_stty() value of
$Expect::Manual_Stty. See $object->manual_stty().
$Expect::Multiline_Matching
Defaults to 1. Affects whether or not expect() uses the /m flag for
doing regular expression matching. If set to 1 /m is used.
This makes a difference when you are trying to match ^ and $. If
you have this on you can match lines in the middle of a page of output
using ^ and $ instead of it matching the beginning and end of the entire
expression. I think this is handy.
CONTRIBUTIONS
Lee Eakin <leakin AT japh.com> has ported the kibitz script from Tcl/Expect to
Perl/Expect.
Jeff Carr <jcarr AT linuxmachines.com> provided a simple example of how handle terminal
window resize events (transmitted via the WINCH signal) in a ssh session.
You can find both scripts in the examples/ subdir. Thanks to both!
Historical notes:
There are still a few lines of code dating back to the inspirational Comm.pl and Chat.pl
modules without which this would not have been possible. Kudos to Eric Arnold
<Eric.Arnold AT Sun.com> and Randal 'Nuke your NT box with one line of perl code'
Schwartz<merlyn AT stonehenge.com> for making these available to the perl public.
As of .98 I think all the old code is toast. No way could this have been done without it
though. Special thanks to Graham Barr for helping make sense of the IO::Handle stuff as
well as providing the highly recommended IO::Tty module.
REFERENCES
Mark Rogaski <rogaski AT att.com> wrote:
"I figured that you'd like to know that Expect.pm has been very useful to AT&T Labs over
the past couple of years (since I first talked to Austin about design decisions). We use
Expect.pm for managing the switches in our network via the telnet interface, and such
automation has significantly increased our reliability. So, you can honestly say that one
of the largest digital networks in existence (AT&T Frame Relay) uses Expect.pm quite
extensively."
FAQ - Frequently Asked Questions
This is a growing collection of things that might help. Please send you questions that
are not answered here to RGiersig AT cpan.org
What systems does Expect run on?
Expect itself doesn't have real system dependencies, but the underlying IO::Tty needs
pseudoterminals. IO::Stty uses POSIX.pm and Fcntl.pm.
I have used it on Solaris, Linux and AIX, others report *BSD and OSF as working.
Generally, any modern POSIX Unix should do, but there are exceptions to every rule.
Feedback is appreciated.
See IO::Tty for a list of verified systems.
Can I use this module with ActivePerl on Windows?
Up to now, the answer was 'No', but this has changed.
You still cannot use ActivePerl, but if you use the Cygwin environment
(http://sources.redhat.com), which brings its own perl, and have the latest IO::Tty (v0.05
or later) installed, it should work (feedback appreciated).
The examples in the tutorial don't work!
The tutorial is hopelessly out of date and needs a serious overhaul. I appologize for
this, I have concentrated my efforts mainly on the functionality. Volunteers welcomed.
How can I find out what Expect is doing?
If you set
$Expect::Exp_Internal = 1;
Expect will tell you very verbosely what it is receiving and sending, what matching it is
trying and what it found. You can do this on a per-command base with
$exp->exp_internal(1);
You can also set
$Expect::Debug = 1; # or 2, 3 for more verbose output
or
$exp->debug(1);
which gives you even more output.
I am seeing the output of the command I spawned. Can I turn that off?
Yes, just set
$Expect::Log_Stdout = 0;
to globally disable it or
$exp->log_stdout(0);
for just that command. 'log_user' is provided as an alias so Tcl/Expect user get a DWIM
experience... :-)
No, I mean that when I send some text to the spawned process, it gets echoed back and I have
to deal with it in the next expect.
This is caused by the pty, which has probably 'echo' enabled. A solution would be to set
the pty to raw mode, which in general is cleaner for communication between two programs
(no more unexpected character translations). Unfortunately this would break a lot of old
code that sends "\r" to the program instead of "\n" (translating this is also handled by
the pty), so I won't add this to Expect just like that. But feel free to experiment with
"$exp->raw_pty(1)".
How do I send control characters to a process?
A: You can send any characters to a process with the print command. To represent a control
character in Perl, use \c followed by the letter. For example, control-G can be
represented with "\cG" . Note that this will not work if you single-quote your string. So,
to send control-C to a process in $exp, do:
print $exp "\cC";
Or, if you prefer:
$exp->send("\cC");
The ability to include control characters in a string like this is provided by Perl, not
by Expect.pm . Trying to learn Expect.pm without a thorough grounding in Perl can be very
daunting. We suggest you look into some of the excellent Perl learning material, such as
the books _Programming Perl_ and _Learning Perl_ by O'Reilly, as well as the extensive
online Perl documentation available through the perldoc command.
My script fails from time to time without any obvious reason. It seems that I am sometimes
loosing output from the spawned program.
You could be exiting too fast without giving the spawned program enough time to finish.
Try adding $exp->soft_close() to terminate the program gracefully or do an expect() for
'eof'.
Alternatively, try adding a 'sleep 1' after you spawn() the program. It could be that pty
creation on your system is just slow (but this is rather improbable if you are using the
latest IO-Tty).
I want to automate password entry for su/ssh/scp/rsh/...
You shouldn't use Expect for this. Putting passwords, especially root passwords, into
scripts in clear text can mean severe security problems. I strongly recommend using other
means. For 'su', consider switching to 'sudo', which gives you root access on a per-
command and per-user basis without the need to enter passwords. 'ssh'/'scp' can be set up
with RSA authentication without passwords. 'rsh' can use the .rhost mechanism, but I'd
strongly suggest to switch to 'ssh'; to mention 'rsh' and 'security' in the same sentence
makes an oxymoron.
It will work for 'telnet', though, and there are valid uses for it, but you still might
want to consider using 'ssh', as keeping cleartext passwords around is very insecure.
I want to use Expect to automate [anything with a buzzword]...
Are you sure there is no other, easier way? As a rule of thumb, Expect is useful for
automating things that expect to talk to a human, where no formal standard applies. For
other tasks that do follow a well-defined protocol, there are often better-suited modules
that already can handle those protocols. Don't try to do HTTP requests by spawning telnet
to port 80, use LWP instead. To automate FTP, take a look at Net::FTP or "ncftp"
(http://www.ncftp.org). You don't use a screwdriver to hammer in your nails either, or do
you?
Is it possible to use threads with Expect?
Basically yes, with one restriction: you must spawn() your programs in the main thread and
then pass the Expect objects to the handling threads. The reason is that spawn() uses
fork(), and perlthrtut:
"Thinking of mixing fork() and threads? Please lie down and wait until the feeling passes."
I want to log the whole session to a file.
Use
$exp->log_file("filename");
or
$exp->log_file($filehandle);
or even
$exp->log_file(\&log_procedure);
for maximum flexibility.
Note that the logfile is appended to by default, but you can specify an optional mode "w"
to truncate the logfile:
$exp->log_file("filename", "w");
To stop logging, just call it with a false argument:
$exp->log_file(undef);
How can I turn off multi-line matching for my regexps?
To globally unset multi-line matching for all regexps:
$Expect::Multiline_Matching = 0;
You can do that on a per-regexp basis by stating "(?-m)" inside the regexp (you need
perl5.00503 or later for that).
How can I expect on multiple spawned commands?
You can use the -i parameter to specify a single object or a list of Expect objects. All
following patterns will be evaluated against that list.
You can specify -i multiple times to create groups of objects and patterns to match
against within the same expect statement.
This works just like in Tcl/Expect.
See the source example below.
I seem to have problems with ptys!
Well, pty handling is really a black magic, as it is extremely system dependend. I have
extensively revised IO-Tty, so these problems should be gone.
If your system is listed in the "verified" list of IO::Tty, you probably have some non-
standard setup, e.g. you compiled your Linux-kernel yourself and disabled ptys. Please
ask your friendly sysadmin for help.
If your system is not listed, unpack the latest version of IO::Tty, do a 'perl
Makefile.PL; make; make test; uname "-a"' and send me the results and I'll see what I can
deduce from that.
I just want to read the output of a process without expect()ing anything. How can I do this?
[ Are you sure you need Expect for this? How about qx() or open("prog|")? ]
By using expect without any patterns to match.
$process->expect(undef); # Forever until EOF
$process->expect($timeout); # For a few seconds
$process->expect(0); # Is there anything ready on the handle now?
Ok, so now how do I get what was read on the handle?
$read = $process->before();
Where's IO::Pty?
Find it on CPAN as IO-Tty, which provides both.
How come when I automate the passwd program to change passwords for me passwd dies before
changing the password sometimes/every time?
What's happening is you are closing the handle before passwd exits. When you close the
handle to a process, it is sent a signal (SIGPIPE?) telling it that STDOUT has gone away.
The default behavior for processes is to die in this circumstance. Two ways you can make
this not happen are:
$process->soft_close();
This will wait 15 seconds for a process to come up with an EOF by itself before killing
it.
$process->expect(undef);
This will wait forever for the process to match an empty set of patterns. It will return
when the process hits an EOF.
As a rule, you should always expect() the result of your transaction before you continue
with processing.
How come when I try to make a logfile with log_file() or set_group() it doesn't print anything
after the last time I run expect()?
Output is only printed to the logfile/group when Expect reads from the process, during
expect(), send_slow() and interconnect(). One way you can force this is to make use of
$process->expect(undef);
and
$process->expect(0);
which will make expect() run with an empty pattern set forever or just for an instant to
capture the output of $process. The output is available in the accumulator, so you can
grab it using $process->before().
I seem to have problems with terminal settings, double echoing, etc.
Tty settings are a major pain to keep track of. If you find unexpected behavior such as
double-echoing or a frozen session, doublecheck the documentation for default settings.
When in doubt, handle them yourself using $exp->stty() and manual_stty() functions. As of
.98 you shouldn't have to worry about stty settings getting fouled unless you use
interconnect or intentionally change them (like doing -echo to get a password).
If you foul up your terminal's tty settings, kill any hung processes and enter 'stty sane'
at a shell prompt. This should make your terminal manageable again.
Note that IO::Tty returns ptys with your systems default setting regarding echoing, CRLF
translation etc. and Expect does not change them. I have considered setting the ptys to
'raw' without any translation whatsoever, but this would break a lot of existing things,
as '\r' translation would not work anymore. On the other hand, a raw pty works much like
a pipe and is more WYGIWYE (what you get is what you expect), so I suggest you set it to
'raw' by yourself:
$exp = new Expect;
$exp->raw_pty(1);
$exp->spawn(...);
To disable echo:
$exp->slave->stty(qw(-echo));
I'm spawning a telnet/ssh session and then let the user interact with it. But screen-oriented
applications on the other side don't work properly.
You have to set the terminal screen size for that. Luckily, IO::Pty already has a method
for that, so modify your code to look like this:
my $exp = new Expect;
$exp->slave->clone_winsize_from(\*STDIN);
$exp->spawn("telnet somehost);
Also, some applications need the TERM shell variable set so they know how to move the
cursor across the screen. When logging in, the remote shell sends a query (Ctrl-Z I
think) and expects the terminal to answer with a string, e.g. 'xterm'. If you really want
to go that way (be aware, madness lies at its end), you can handle that and send back the
value in $ENV{TERM}. This is only a hand-waving explanation, please figure out the
details by yourself.
I set the terminal size as explained above, but if I resize the window, the application does
not notice this.
You have to catch the signal WINCH ("window size changed"), change the terminal size and
propagate the signal to the spawned application:
my $exp = new Expect;
$exp->slave->clone_winsize_from(\*STDIN);
$exp->spawn("ssh somehost);
$SIG{WINCH} = \&winch;
sub winch {
$exp->slave->clone_winsize_from(\*STDIN);
kill WINCH => $exp->pid if $exp->pid;
$SIG{WINCH} = \&winch;
}
$exp->interact();
There is an example file ssh.pl in the examples/ subdir that shows how this works with
ssh. Please note that I do strongly object against using Expect to automate ssh login, as
there are better way to do that (see ssh-keygen).
I noticed that the test uses a string that resembles, but not exactly matches, a well-known
sentence that contains every character. What does that mean?
That means you are anal-retentive. :-) [Gotcha there!]
I get a "Could not assign a pty" error when running as a non-root user on an IRIX box?
The OS may not be configured to grant additional pty's (pseudo terminals) to non-root
users. /usr/sbin/mkpts should be 4755, not 700 for this to work. I don't know about
security implications if you do this.
How come I don't notice when the spawned process closes its stdin/out/err??
You are probably on one of the systems where the master doesn't get an EOF when the slave
closes stdin/out/err.
One possible solution is when you spawn a process, follow it with a unique string that
would indicate the process is finished.
$process = Expect->spawn('telnet somehost; echo ____END____');
And then $process->expect($timeout,'____END____','other','patterns');
Source Examples
How to automate login
my $telnet = new Net::Telnet ("remotehost") # see Net::Telnet
or die "Cannot telnet to remotehost: $!\n";;
my $exp = Expect->exp_init($telnet);
# deprecated use of spawned telnet command
# my $exp = Expect->spawn("telnet localhost")
# or die "Cannot spawn telnet: $!\n";;
my $spawn_ok;
$exp->expect($timeout,
[
qr'login: $',
sub {
$spawn_ok = 1;
my $fh = shift;
$fh->send("$username\n");
exp_continue;
}
],
[
'Password: $',
sub {
my $fh = shift;
print $fh "$password\n";
exp_continue;
}
],
[
eof =>
sub {
if ($spawn_ok) {
die "ERROR: premature EOF in login.\n";
} else {
die "ERROR: could not spawn telnet.\n";
}
}
],
[
timeout =>
sub {
die "No login.\n";
}
],
'-re', qr'[#>:] $', #' wait for shell prompt, then exit expect
);
How to expect on multiple spawned commands
foreach my $cmd (@list_of_commands) {
push @commands, Expect->spawn($cmd);
}
expect($timeout,
'-i', \@commands,
[
qr"pattern", # find this pattern in output of all commands
sub {
my $obj = shift; # object that matched
print $obj "something\n";
exp_continue; # we don't want to terminate the expect call
}
],
'-i', $some_other_command,
[
"some other pattern",
sub {
my ($obj, $parmref) = @_;
# ...
# now we exit the expect command
},
\$parm
],
);
How to propagate terminal sizes
my $exp = new Expect;
$exp->slave->clone_winsize_from(\*STDIN);
$exp->spawn("ssh somehost);
$SIG{WINCH} = \&winch;
sub winch {
$exp->slave->clone_winsize_from(\*STDIN);
kill WINCH => $exp->pid if $exp->pid;
$SIG{WINCH} = \&winch;
}
$exp->interact();
HOMEPAGE
http://sourceforge.net/projects/expectperl/
MAILING LISTS
There are two mailing lists available, expectperl-announce and expectperl-discuss, at
http://lists.sourceforge.net/lists/listinfo/expectperl-announce
and
http://lists.sourceforge.net/lists/listinfo/expectperl-discuss
BUG TRACKING
You can use the CPAN Request Tracker http://rt.cpan.org/ and submit new bugs under
http://rt.cpan.org/Ticket/Create.html?Queue=Expect
AUTHORS
(c) 1997 Austin Schutz <ASchutz AT users.net> (retired)
expect() interface & functionality enhancements (c) 1999-2006 Roland Giersig.
This module is now maintained by Roland Giersig <RGiersig AT cpan.org>
LICENSE
This module can be used under the same terms as Perl.
DISCLAIMER
THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT
NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
In other words: Use at your own risk. Provided as is. Your mileage may vary. Read the
source, Luke!
And finally, just to be sure:
Any Use of This Product, in Any Manner Whatsoever, Will Increase the Amount of Disorder in
the Universe. Although No Liability Is Implied Herein, the Consumer Is Warned That This
Process Will Ultimately Lead to the Heat Death of the Universe.
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