.TH empty 1 "March, 05 2006"
.SH NAME
empty \- run processes under pseudo-terminal sessions
.SH SYNOPSIS
.br
.B empty
\-f [\-i fifo1 \-o fifo2] [-p file.pid] [\-L file.log] command [command args]
.br
.B empty
\-w [\-Sv] [\-t n] [\-i fifo2 \-o fifo1] key1 [answer1] ... [keyX answerX]
.br
.B empty
\-s [\-Sc] \-o fifo1 [request]
.br
.B empty
\-r [\-b size] [\-t n] [\-i fifo2]
.br
.B empty
\-l
.br
.B empty
\-k [pid] [signal]
.br
.B empty
\-h
.SH DESCRIPTION
.B empty
is an utility that provides a simple interface to execute and/or interact with processes under pseudo-terminal sessions. This tool is definitely useful in programming of shell scripts which are used to communicate with interactive programs like telnet or ftp. In some cases
.B empty
can be a substitution for TCL/expect or other similar programming tools.
.PP
There are several common forms of command lines for
.B empty.
But the first execution of
.B empty
is usually a start in the daemon mode to
.B fork
a new 
.B command 
(process) under PTY-session. This can be done with 
.B \-f
key. 
An interface for the input and output data channels of the forked process is performed by two fifo files which names may be specified with
.B \-i 
and 
.B \-o 
keys. These files are automatically created/deleted any time you start/exit
.B empty
daemon, so you must not create them manually. If you did not specify these fifo files in the command line,
.B empty
names them by itself basing on its PID and PID of forked PTY process.
.PP
At this point any application can easily communicate with forked process by writing data to the input fifo and reading answers from the output fifo, see
.B EXAMPLES 
section for the details. To simplify this operations,
.B empty
offers an interface to just
.B send
any data (use
.B \-s
key), or even to 
.B watch
the output fifo for multiple 
.B keyphrases
and reply to the input fifo with one of the
.B responses
(see
.B \-w
key).
.PP
.B Note!
Input fifo for
.B empty -f ...
is usually an output fifo for
.B empty -w 
and 
.B empty -s
forms. And output fifo of
.B empty -f ...
is an input fifo for
.B empty -w ...
.PP
If something goes wrong the forked process may be 
.B killed
by the standard kill command, or using
.B \-k
key of
.B empty.
See
.B \-p 
option to save PID of empty daemon process.
.PP
The following options are available:
.TP 12
\-f
fork, spawn, start or execute a new process specified by the
.B command
and its arguments. If you omit fifo files,
.B empty
with its job control algorithm will create them under /tmp directory using this templates: empty.PPID.PID.in and empty.PPID.PID.out, here PPID is usually your shell system process ID and PID is system process ID of empty-daemon.
.TP
\-s
send data (request) to the forked process. If fifo file was not specified with
.B \-o
key,
.B empty 
will try to find an automatically created fifo file it in /tmp directory. Instead of command line you can send your
.B request
or data directly to standard input (stdin) of
.B empty
.TP
\-w
.B watch
for one or more
.B keyphrases
and if specified send the appropriated
.B response
to the input fifo.
If 
.B response
is not set,
.B empty
waits for the proper
.B keyphrase
then exits. With
.B \-w
key
.B empty
returns the number of matched keyphrase-response pair, or 255 if fails to find this match (see -t key for details of possible exit on timeout).
.TP
\-r
read from output FIFO one line (default) or one block of data (if 
.B \-b size 
was specified). If 
.B \-t n
key was placed, exit on timeout.
.TP
\-l
list automatically created jobs by your shell.
.B NB!
Your custom jobs, which fifo files you specified with 
.B \-i 
and
.B \-o
keys, are not displayed. So if you did not specify fifo files with
.B -i
and 
.B -o 
keys all 
operations are done under the job marked
.B current
.TP
\-k 
send
.B signal
to the process with
.B pid.
If you did not specify pid, 
.B empty
tries to find it within the list of automatically created jobs. If
.B signal
is omitted the default SIGTERM is used.
.TP
\-h
print short help message and exit
.TP
\-i fifo1
a fifo file, which is used as input for a forked process.
.TP
\-o fifo2
a fifo file, which is used as output for a forked process.
.TP
\-L file.log
This option allows to log the whole
.B empty
session to a file. Marks >>> and <<< show the directions of data flow.
.TP
\-\-logfile-mode=mode
This option allows to choose the mode of the log file created with the -L option.
The default mode is 0600.
.TP
\-p file.pid
Save PID of empty daemon process to a file
.TP
\-t n
If input FIFO is empty, wait for n seconds (default is 10) to receive the
.B
keyphrase
then exit on timeout with 255 code.
.TP
\-c
force
.B empty
to use stdin for data or requests.
.TP
\-S
Strip the last character from the input. Works with -s and -w keys
.TP
\-v
kvazi verbose mode. Show all contents of received buffer.
.SH EXAMPLES
.TP 0 
Start a new PTY-session with telnet to localhost:
.nf
	empty -f -i in.fifo -o out.fifo -p empty.pid -L empty.log telnet localhost
.fi
.TP
Interact with telnet:
.nf
	empty \-w \-i out.fifo \-o in.fifo ogin 'my_user\\n'
	empty \-w \-i out.fifo \-o in.fifo assword 'my_password\\n'
.fi
.TP
Send commands to telnet with empty:
.nf
	empty \-s \-o in.fifo who
	empty \-s \-o in.fifo "ls \-la /\\n"
.fi
.TP
The same using STDIN:
.nf
	echo who | empty \-s \-o in.fifo
	echo "ls \-la /" | empty \-s \-o in.fifo
.fi
.TP
Just cat output from telnet:
.nf
	cat out.fifo
.fi
.TP
Read one line from out.fifo:
.nf
	empty \-r -i out.fifo 
.fi
.TP
Send commands to telnet with ordinary echo:
.nf
	echo "who am i" > in.fifo
	echo "uname -a" > in.fifo
.fi
.TP
Kill a process with PID 1234:
.nf
	empty -k 1234
or
	kill 1234
.nf
.TP
Telnet session with automatically created jobs:
.nf
	empty -f telnet localhost
.fi
.TP
Interact with telnet using job control:
.nf
	empty \-w ogin 'my_user\\n'
	empty \-w assword 'my_password\\n'
.fi
.TP
List automatically created jobs:
.nf
	empty \-l

	PPID    PID     TYPE    FILENAME
	479     706     in      /tmp/empty.479.706.in
	479     706     out     /tmp/empty.479.706.out
	479     711     in      /tmp/empty.479.711.in
	479     711     out     /tmp/empty.479.711.out

	479     711     current
.fi
.SH SECURITY
It is considered insecure to send a password in the command line like this:
.nf
	
	empty \-w assword 'my_password\\n'

.fi
or like this:
.nf

	empty \-s 'my_password\\n'

.fi

The reason is that the command line arguments are visible to the system while
.B empty
is running. Any local user can see them with ps(1), sometimes they are visible
even remotely with finger(1).
Also your server may have some monitoring tools which may store the output
from ps(1) in their logs. There are also other, more complicated ways
to compromise this information. Generally, you should take command line arguments
as (possibly) visible to every one unless you really know what you're doing.

.B empty
with '-s' flag runs quickly in most cases, but still it can hang for a number
of reasons (like fifo overloading), and even if it runs quick you still cannot
be sure that no one will see its command line arguments even in this short time.
.B empty
with '-w' flag is even worse because it must wait for the keyphrase.

A better way to send the password to the supervised program
is to read it from file:
.nf

	empty \-s [common options] <./password-file

.fi
or from a pipe:
.nf

	get-password-of-user "$user" |empty -s [common options]

.fi
You should still make sure that you do not send any password via command line
while creating this file, and certainly you should set some safe permissions
to this file AND its directory (with the parent directories) before reading
the password from the file OR writing the password to it.

Another possible way is to use your shell's builtin (but see below):
.nf

	echo "$password" |empty \-s [common options]

.fi
Many shells like bash(1), csh(1) and FreeBSD's sh(1) do not call external
echo(1) command but use their own builtin echo command. Since no external
command is started (the shell itself does all that echo(1) must do),
nothing is shown in the process list. It is beyond this manual page to discuss
the way to make sure that your shell uses the builtin command.
.SH RETURN VALUES
If any error occurs
.B empty
usually exits with code 255. Otherwise zero or some positive value (see 
.B \-w
key) is returned. 
.SH SEE ALSO
expect(1), chat(8)
.SH AUTHOR
.B empty
was made by Mikhail E. Zakharov. This software was based on the basic idea of pty version 4.0 Copyright (c) 1992, Daniel J. Bernstein but no code was ported from pty4.
SECURITY section of this manual page was contributed by Sergey Redin.