lp - send files to a printer
lp [-c] [-d dest] [-n copies] [-msw] [-o option]... [-t title] [file...]
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.
The lp utility shall conform to XBD Utility Syntax Guidelines .
The following options shall be supported:
- 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.
- 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.
- Suppress messages from lp.
- -t title
- Write title on the banner page of the output.
- 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.
The following operand shall be supported:
- 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.
The standard input shall be used only if no file operands are specified, or if a file operand is '-'. See the INPUT FILES section.
The input files shall be text files.
The following environment variables shall affect the execution of lp:
- Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- 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).
- 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.
- Determine the format and contents of date and time strings displayed in the lp banner page, if any.
- 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.
- [XSI] Determine the location of message catalogs for the processing of LC_MESSAGES.
- 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.
- 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.
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.
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
- All input files were processed successfully.
- No output device was available, or an error occurred.
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.1-2017 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.
To print file file:lp -c file
To print multiple files with headers:pr file1 file2 | lp
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.1-2017 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.1-2017 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.1-2017.
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.1-2017 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.1-2017 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.
XBD Environment Variables, Utility Syntax Guidelines
First released in Issue 2.
The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:
In the DESCRIPTION, the requirement to associate a unique request ID, and the normal generation of a banner page is added.
In the OPTIONS section:
The -d dest description is expanded, but references to lpstat are removed.
The -m, -o, -s, -t, and -w options are added.
In the ENVIRONMENT VARIABLES section, LC_TIME may now affect the execution.
The STDOUT section is added.
The normative text is reworded to avoid use of the term "must" for application requirements.
The TZ entry is added to the ENVIRONMENT VARIABLES section.
SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.
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