How can I show all input and output with Expect.pm (Perl)? - perl

Question

Here is a little Perl server. It displays (1), accepts a line of input, then displays (2), etc. If you type "error" or "commit", it gives a custom message. If you type "exit", it quits. Otherwise, it just endlessly takes lines of input.
use strict;
use warnings;
$|++;
my $counter = 1;
print "($counter) ";
while (<STDIN>) {
chomp;
if ($_ eq "error") {print "Error on command #$counter\n";}
if ($_ eq "commit") {print "Committing data\n";}
if ($_ eq "exit") {print "Exiting program...\n"; exit;}
$counter++;
print "($counter) ";
}
Now, here is an Expect.pm client script to interact with the server script by typing in various lines.
use strict;
use warnings;
use Expect;
$|++;
my $exp = new Expect;
$exp->raw_pty(1);
$exp->log_file("/tmp/expect.out");
$exp->log_stdout(1);
my #commands = (
"This is the first command",
"Here is the second command",
"error",
"commit",
"This is the last command",
"exit",
);
$exp->spawn("./expecttest_server.pl");
foreach my $command (#commands) {
print "$command\n";
$exp->send("$command\n");
$exp->expect(1, '-re','\(\d+\)');
}
$exp->soft_close();
What I want is to be able to store the entire session from start to finish, including everything the server script generated, and everything the Expect.pm script sent.
That is, I want my client script to be able to return output like this, which is what you would see if you ran and interacted with the server script manually:
(1) This is the first command
(2) Here is the second command
(3) error
Error on command #3
(4) commit
Committing data
(5) This is the last command
(6) exit
Exiting program...
But the STDOUT display that comes from running the client script looks like this:
This is the first command
(1) (2) Here is the second command
error
(3) Error on command #3
(4) commit
This is the last command
Committing data
(5) (6) exit
Exiting program...
and the file specified by $exp->log_file (tmp/expect.out) shows this:
(1) (2) (3) Error on command #3
(4) Committing data
(5) (6) Exiting program...
I've tried experimenting by logging various combinations of the command itself + the before_match and after_match variables returned by $exp->expect(). But so far I haven't gotten the right combination. And it seems like an awfully clunky way to get what I'm looking for.
So, what's the best practice for capturing the entirety of an Expect.pm session?
Thanks to anyone who can help!

Answer 1

When run on the command line, your server prints
(1)
to stdout immediately and waits for input.
However, when you create an Expect object, you are actually setting up a PTY (a pseudo terminal). Any processes you spawn will have their stdin and stdout connected to this PTY, not to the TTY that your shell is connected to. This means that it's up to your Expect object whether output from the spawned process is displayed or not; it will not be displayed automatically.
When you spawn a process, the Expect object holds onto any output in an input buffer. When you send a string to the process, any additional output that is generated will be read into the buffer. If the PTY has echoing enabled (the default), the string you send will be echoed back, but the contents of the Expect object's buffer will not.
When you call the expect method, Expect waits until a matching string appears in the input buffer. If a match is found before the timeout expires, expect returns and prints the matching string.
So, all you need to do is call expect before sending your first command, something like this:
Server
use strict;
use warnings;
$| = 1;
my $counter = 1;
do {
print "($counter) ";
$counter++;
} while (<>);
Client
use strict;
use warnings;
use Expect;
$| = 1;
my $exp = Expect->new;
my $server = './expect_server';
$exp->spawn($server);
my #commands = qw(foo bar baz);
foreach my $command (#commands) {
$exp->expect(1, '-re', '\(\d+\)');
$exp->send("$command\r");
}
$exp->soft_close;
Output
(1) foo
(2) bar
(3) baz
(4)
Note that this is the exact same process you would use when interacting with a process manually: wait for the prompt, then type your command.