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PROGRAM:

NAME


lp — send files to a printer

SYNOPSIS


lp [−c] [−d dest] [−n copies] [−msw] [−o option]... [−t title] [file...]

DESCRIPTION


The lp utility shall copy the input files to an output destination in an unspecified
manner. The default output destination should be to a hardcopy device, such as a printer
or microfilm recorder, that produces non-volatile, human-readable documents. If such a
device is not available to the application, or if the system provides no such device, the
lp utility shall exit with a non-zero exit status.

The actual writing to the output device may occur some time after the lp utility
successfully exits. During the portion of the writing that corresponds to each input file,
the implementation shall guarantee exclusive access to the device.

The lp utility shall associate a unique request ID with each request.

Normally, a banner page is produced to separate and identify each print job. This page may
be suppressed by implementation-defined conditions, such as an operator command or one of
the −o option values.

OPTIONS


The lp utility shall conform to the Base Definitions volume of POSIX.1‐2008, Section 12.2,
Utility Syntax Guidelines.

The following options shall be supported:

−c Exit only after further access to any of the input files is no longer required.
The application can then safely delete or modify the files without affecting the
output operation. Normally, files are not copied, but are linked whenever
possible. If the −c option is not given, then the user should be careful not to
remove any of the files before the request has been printed in its entirety. It
should also be noted that in the absence of the −c option, any changes made to
the named files after the request is made but before it is printed may be
reflected in the printed output. On some implementations, −c may be on by
default.

−d dest Specify a string that names the destination (dest). If dest is a printer, the
request shall be printed only on that specific printer. If dest is a class of
printers, the request shall be printed on the first available printer that is a
member of the class. Under certain conditions (printer unavailability, file
space limitation, and so on), requests for specific destinations need not be
accepted. Destination names vary between systems.

If −d is not specified, and neither the LPDEST nor PRINTER environment variable
is set, an unspecified destination is used. The −d dest option shall take
precedence over LPDEST, which in turn shall take precedence over PRINTER.
Results are undefined when dest contains a value that is not a valid destination
name.

−m Send mail (see mailx) after the files have been printed. By default, no mail is
sent upon normal completion of the print request.

−n copies Write copies number of copies of the files, where copies is a positive decimal
integer. The methods for producing multiple copies and for arranging the
multiple copies when multiple file operands are used are unspecified, except
that each file shall be output as an integral whole, not interleaved with
portions of other files.

−o option Specify printer-dependent or class-dependent options. Several such options may
be collected by specifying the −o option more than once.

−s Suppress messages from lp.

−t title Write title on the banner page of the output.

−w Write a message on the user's terminal after the files have been printed. If the
user is not logged in, then mail shall be sent instead.

OPERANDS


The following operand shall be supported:

file A pathname of a file to be output. If no file operands are specified, or if a
file operand is '−', the standard input shall be used. If a file operand is
used, but the −c option is not specified, the process performing the writing to
the output device may have user and group permissions that differ from that of
the process invoking lp.

STDIN


The standard input shall be used only if no file operands are specified, or if a file
operand is '−'. See the INPUT FILES section.

INPUT FILES


The input files shall be text files.

ENVIRONMENT VARIABLES


The following environment variables shall affect the execution of lp:

LANG Provide a default value for the internationalization variables that are unset or
null. (See the Base Definitions volume of POSIX.1‐2008, Section 8.2,
Internationalization Variables for the precedence of internationalization
variables used to determine the values of locale categories.)

LC_ALL If set to a non-empty string value, override the values of all the other
internationalization variables.

LC_CTYPE Determine the locale for the interpretation of sequences of bytes of text data
as characters (for example, single-byte as opposed to multi-byte characters in
arguments and input files).

LC_MESSAGES
Determine the locale that should be used to affect the format and contents of
diagnostic messages written to standard error and informative messages written
to standard output.

LC_TIME Determine the format and contents of date and time strings displayed in the lp
banner page, if any.

LPDEST Determine the destination. If the LPDEST environment variable is not set, the
PRINTER environment variable shall be used. The −d dest option takes precedence
over LPDEST. Results are undefined when −d is not specified and LPDEST contains
a value that is not a valid destination name.

NLSPATH Determine the location of message catalogs for the processing of LC_MESSAGES.

PRINTER Determine the output device or destination. If the LPDEST and PRINTER
environment variables are not set, an unspecified output device is used. The −d
dest option and the LPDEST environment variable shall take precedence over
PRINTER. Results are undefined when −d is not specified, LPDEST is unset, and
PRINTER contains a value that is not a valid device or destination name.

TZ Determine the timezone used to calculate date and time strings displayed in the
lp banner page, if any. If TZ is unset or null, an unspecified default timezone
shall be used.

ASYNCHRONOUS EVENTS


Default.

STDOUT


The lp utility shall write a request ID to the standard output, unless −s is specified.
The format of the message is unspecified. The request ID can be used on systems supporting
the historical cancel and lpstat utilities.

STDERR


The standard error shall be used only for diagnostic messages.

OUTPUT FILES


None.

EXTENDED DESCRIPTION


None.

EXIT STATUS


The following exit values shall be returned:

0 All input files were processed successfully.

>0 No output device was available, or an error occurred.

CONSEQUENCES OF ERRORS


Default.

The following sections are informative.

APPLICATION USAGE


The pr and fold utilities can be used to achieve reasonable formatting for the
implementation's default page size.

A conforming application can use one of the file operands only with the −c option or if
the file is publicly readable and guaranteed to be available at the time of printing. This
is because POSIX.1‐2008 gives the implementation the freedom to queue up the request for
printing at some later time by a different process that might not be able to access the
file.

EXAMPLES


1. To print file file:

lp −c file

2. To print multiple files with headers:

pr file1 file2 | lp

RATIONALE


The lp utility was designed to be a basic version of a utility that is already available
in many historical implementations. The standard developers considered that it should be
implementable simply as:

cat "$@" > /dev/lp

after appropriate processing of options, if that is how the implementation chose to do it
and if exclusive access could be granted (so that two users did not write to the device
simultaneously). Although in the future the standard developers may add other options to
this utility, it should always be able to execute with no options or operands and send the
standard input to an unspecified output device.

This volume of POSIX.1‐2008 makes no representations concerning the format of the printed
output, except that it must be ``human-readable'' and ``non-volatile''. Thus, writing by
default to a disk or tape drive or a display terminal would not qualify. (Such
destinations are not prohibited when −d dest, LPDEST, or PRINTER are used, however.)

This volume of POSIX.1‐2008 is worded such that a ``print job'' consisting of multiple
input files, possibly in multiple copies, is guaranteed to print so that any one file is
not intermixed with another, but there is no statement that all the files or copies have
to print out together.

The −c option may imply a spooling operation, but this is not required. The utility can be
implemented to wait until the printer is ready and then wait until it is finished. Because
of that, there is no attempt to define a queuing mechanism (priorities, classes of output,
and so on).

On some historical systems, the request ID reported on the STDOUT can be used to later
cancel or find the status of a request using utilities not defined in this volume of
POSIX.1‐2008.

Although the historical System V lp and BSD lpr utilities have provided similar
functionality, they used different names for the environment variable specifying the
destination printer. Since the name of the utility here is lp, LPDEST (used by the System
V lp utility) was given precedence over PRINTER (used by the BSD lpr utility). Since
environments of users frequently contain one or the other environment variable, the lp
utility is required to recognize both. If this was not done, many applications would send
output to unexpected output devices when users moved from system to system.

Some have commented that lp has far too little functionality to make it worthwhile.
Requests have proposed additional options or operands or both that added functionality.
The requests included:

* Wording requiring the output to be ``hardcopy''

* A requirement for multiple printers

* Options for supporting various page-description languages

Given that a compliant system is not required to even have a printer, placing further
restrictions upon the behavior of the printer is not useful. Since hardcopy format is so
application-dependent, it is difficult, if not impossible, to select a reasonable subset
of functionality that should be required on all compliant systems.

The term unspecified is used in this section in lieu of implementation-defined as most
known implementations would not be able to make definitive statements in their conformance
documents; the existence and usage of printers is very dependent on how the system
administrator configures each individual system.

Since the default destination, device type, queuing mechanisms, and acceptable forms of
input are all unspecified, usage guidelines for what a conforming application can do are
as follows:

* Use the command in a pipeline, or with −c, so that there are no permission problems
and the files can be safely deleted or modified.

* Limit output to text files of reasonable line lengths and printable characters and
include no device-specific formatting information, such as a page description
language. The meaning of ``reasonable'' in this context can only be answered as a
quality-of-implementation issue, but it should be apparent from historical usage
patterns in the industry and the locale. The pr and fold utilities can be used to
achieve reasonable formatting for the default page size of the implementation.

Alternatively, the application can arrange its installation in such a way that it requires
the system administrator or operator to provide the appropriate information on lp options
and environment variable values.

At a minimum, having this utility in this volume of POSIX.1‐2008 tells the industry that
conforming applications require a means to print output and provides at least a command
name and LPDEST routing mechanism that can be used for discussions between vendors,
application developers, and users. The use of ``should'' in the DESCRIPTION of lp clearly
shows the intent of the standard developers, even if they cannot mandate that all systems
(such as laptops) have printers.

This volume of POSIX.1‐2008 does not specify what the ownership of the process performing
the writing to the output device may be. If −c is not used, it is unspecified whether the
process performing the writing to the output device has permission to read file if there
are any restrictions in place on who may read file until after it is printed. Also, if −c
is not used, the results of deleting file before it is printed are unspecified.

FUTURE DIRECTIONS


None.

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