postio.1

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

.TH POSTIO 1 "DWB 3.2"
.SH NAME
.B postio
\- serial interface for PostScript printers
.SH SYNOPSIS
\*(mBpostio\f1
.OP \-l line
.OP "" options []
.OP "" files []
.SH DESCRIPTION
.B postio
sends
.I files
to the PostScript printer attached to
.IR line .
If no
.I files
are specified the standard input is sent.
The first group of
.I options
should be sufficient for most applications:
.TP 0.75i
.OP \-b speed
Transmit data over
.I line
at baud rate
.I speed.
Recognized baud rates are 1200, 2400, 4800, 9600, and 19200.
The default
.I speed
is 9600 baud.
.TP
.OP \-c
Do not send
.MR ^C s
(interrupts) to the printer,
which means
.B postio
does not force a busy printer into the idle state.
.TP
.OP \-l line
Connect to printer attached to
.IR line .
In most cases there is no default and
.B postio
must be able to read and write
.IR line .
If
.I line
does not begin with
.MW /
it is treated as a Datakit destination.
.TP
.OP \-q
Prevents status queries while
.I files
are being sent to the printer.
When status queries are disabled a dummy message is appended
to the log file before each block is transmitted.
.TP
.OP \-B num
Set internal buffer size for reading and writing
.I files
to
.I num
bytes
(default is 2048 bytes).
.TP
.OP \-D
Enable debug mode.
Guarantees that everything read on
.I line
will be added to the log file (standard error by default).
.TP
.OP \-L file
Data received on
.I line
gets put in
.IR file .
The default log
.I file
is standard error.
Printer or status messages that do not indicate a change in state
are not normally written to
.I file
but can be forced out using the
.OP \-D
option.
.TP
.OP \-P string
Send
.I string
to the printer before any of the input files.
The default
.I string
is simple PostScript code that disables timeouts.
.TP
.OP \-R num
Run
.B postio
as a single process if
.I num
is 1 or as separate read and write processes if
.I num
is 2.
By default
.B postio
runs as a single process.
.PP
The next two
.I options
are provided for users who expect to run
.B postio
on their own.
Neither is suitable for use in spooler interface
programs:
.TP 0.35i
.OP \-i
Run the program in interactive mode.
Any
.I files
are sent first and followed by the standard input.
Forces separate read and write processes
and overrides many other options.
To exit interactive mode use your interrupt or quit character.
To get a friendly interactive connection with the printer type
.MW executive
on a line by itself.
.TP
.OP \-t
Data received on
.I line
and not recognized as printer or status information is written to
the standard output.
Forces separate read and write processes.
Convenient if you have a PostScript program that
will be returning useful data to the host.
.PP
The last option is not generally recommended and should only
be used if all else fails to provide a reliable connection:
.TP 0.35i
.OP \-S
Slow the transmission of data to the printer.
Severely limits throughput, runs as a single process,
disables the
.OP \-q
option, limits the internal buffer size to 1024 bytes,
can use an excessive amount of
.SM CPU
time, and does nothing in interactive mode.
.PP
Best performance is usually obtained by using
a large internal buffer
.OP -B "" ) (
and by running the program as separate read and write processes
.OP \-R2 "" ). (
Inability to fork the additional process causes
.B postio
to continue as a single read/write process.
When one process is used, only data sent to the printer is flow-controlled.
.PP
The options are not all mutually exclusive.
The
.OP \-i
option always wins, selecting its own settings for whatever is
needed to run interactive mode, independent of anything else
found on the command line.
Interactive mode runs as separate read and write processes
and few of the other
.I options
accomplish anything in the presence of the
.OP \-i
option.
The
.OP \-t
option needs a reliable two way connection to the printer and
therefore tries to force separate read and write processes.
The
.OP \-S
option relies on the status query mechanism, so
.OP \-q
is disabled and the program runs as a single process.
.PP
In most cases
.B postio
starts by making a connection to
.I line
and then attempts to force the printer into the
.SM IDLE
state by sending an appropriate sequence of
.MW ^T
(status query), 
.MW ^C
(interrupt), and
.MW ^D
(end of job) characters.
When the printer goes
.SM IDLE
.I files
are transmitted along with an occasional
.MW ^T
(unless the
.OP \-q
option was used).
After all the
.I files
are sent the program waits until it is reasonably sure the
job is complete.
Printer generated error messages received at any time
except while establishing the initial connection
(or when running interactive mode) cause
.B postio
to exit with a non-zero status.
In addition to being added to the log file, printer error messages
are also echoed to standard error.
.SH EXAMPLES
Run as a single process at 9600 baud and send
.I file1
and
.I file2
to the printer attached to
.MR /dev/tty01 :
.EX
postio -l /dev/tty01  \f2file1  file2
.EE
Same as above except two processes are used,
the internal buffer is set to 4096 bytes,
and data returned by the printer gets put in file
.MR log :
.EX
postio -R2 -B4096 -l/dev/tty01 -Llog  \f2file1  file2
.EE
Establish an interactive connection with the printer at Datakit
destination
.MR my/printer :
.EX
postio -i -l my/printer
.EE
Send file
.MW program
to the printer connected to
.MR /dev/tty22 ,
recover any data in file
.MR results ,
and put log messages in file
.MR log :
.EX
postio -t -l /dev/tty22 -L log program >results
.EE
.SH DIAGNOSTICS
A 0 exit status is returned if the files ran successfully.
System errors (e.g., ``can't open the line'') set the low order
bit in the exit status, while PostScript errors set bit 1.
An exit status of 2 usually means the printer
detected a PostScript error in the input
.IR files .
.SH WARNINGS
.PP
The input
.I files
are handled as a single PostScript job.
Sending several different jobs, each with their own internal
end of job mark
.RM ( ^D )
is not guaranteed to work properly.
.B postio
may quit before all the jobs have completed and could be restarted
before the last one finishes.
.PP
All the capabilities described above may not be available on every
machine or even across the different versions of
.SM UNIX
that are currently supported by the program.
For example, the code needed to connect to a Datakit destination may only
work on System\ V and may require that the
.SM DKHOST
software package be available at compile time.
.PP
There may be no default
.I line
so using
.OP \-l
option is strongly recommended.
If omitted
.B postio
may attempt to connect to the printer using the standard output.
If Datakit is involved the
.OP \-b
may be ineffective and attempts by
.B postio
to flow control data in both directions may not work.
The
.OP \-q
option can help if the printer is connected to \s-1RADIAN\s+1.
The
.OP \-S
option is not generally recommended and should only be used if
all else fails to establish a reliable connection.
.SH SEE ALSO
.BR buildtables (1),
.BR dpost (1),
.BR postdaisy (1),
.BR postdmd (1),
.BR postmd (1),
.BR postprint (1),
.BR postreverse (1),
.BR posttek (1),
.BR printfont (1)