Appendix E. PDL Transform Language

Table of Contents

Definitions
Writing a transform
Examples
Transform Language Functions & Specification
Test Mode
Tips & Tricks

PDL Transforms are an advanced PaperCut MF feature. This appendix is written assuming the reader has an understanding of printer description languages, and a basic knowledge of scripting.

A transform is a process that defines how to convert an input into a different output. In PaperCut MF, transforms are defined as simple scripts. There are a number of reasons for performing transforms on a print job. These include:

Extending Compatibility

The output produced by one driver (such as PostScript) may not work on other printer brands without modification. For example, "TRAY = 1" on one printer may map to "TRAY = UPPER" on another. Transforms can be used to automatically make this adjustment to a print job. This is particularly important in a Find-Me printing environment where a job rendered by one driver may not print correctly on another printer type without modifying the print job.

Modify Behaviour/Output

Much is possible with the power of transforms. Maybe it’s always enabling the "eco print" mode when an email is printed, or automatically removing the "stapling" option if accidently selected on a printer the does not support stapling. Another use-case is "virtual stationery". Legacy reports could for example have a logo automatically added to each page.

Of note, PaperCut performs page analysis before transforms are applied. As such, a color logo added to a grayscale page, will be recorded in PaperCut as grayscale.

Definitions

Before covering the details of the transform language, it’s important to understand the following terms:

Page Description Language (PDL)

A language used to describe the appearance of a printed page e.g. PostScript, Printer Control Language (PCL).

Printer Job Language (PJL) Header

Attributes in a PJL header define print job characteristics such as duplex, color, paper sizes, or media trays. Many printers rely on a PJL header, though many attributes are printer/manufacturer specific.

Transform Script

A transform script defines a transform process to apply to a print job’s PDL. Transform scripts are written in a very simple scripting Domain Specific Language (DSL).

Source & Target

The transform process refers to source and target print queues. A desired transform is applied when a job is transferred from a specific source queue (a global queue) to a specific target queue.

Writing a transform

Transforms are text files placed in a location (directory structure) that determines when the script applies. The file’s name and location must conform to the following path:

    [install-path]/providers/print/[platform]/transforms/custom/[language]/[source]/[target].transform
                

language - the PDL language of the print job (e.g. Postscript).
source - the name of the queue that first received the print job (e.g. a global queue).
target - the name of the queue the job is being transferred to print to.

For example, to apply a transform when a job is transferred from the queue named "Global Queue" to "Printer A", the transform file should be located at:

    [install-path]/providers/print/[platform]/transforms/custom/postscript/global queue/printer a.transform
                 

Matching rules for running a transform script

The following steps select the transform script to run for a redirection from printer type source to printer type destination which both use printer language language.

  1. Look first in the the custom directory then in the system directory.

  2. Find the subdirectory whose name matches language e.g. if language is PostScript then look in custom/postscript.

  3. Find the subdirectory whose name matches source. e.g. if source is PaperCut Global PostScript then look in custom/postscript/pc-win. (NOTE: On PaperCut MF systems, pc-win is an alias that matches printer type PaperCut Global PostScript).

  4. Find the file whose name matches destination. e.g. if destination is HP Color LaserJet then look for custom/postscript/pc-win/hp.color.laserjet.transform. This does not exist so backtrack.

  5. Backtracking takes us to custom/postscript/pc-win/default.transform which does not exist, then custom/postscript/default.transform which does not exist, then system/postscript/pc-win/hp.color.laserjet.type.transform which does exist. (NOTE: printer type is matched against *.type.transform and printer name is matched agaist *.name.transform before printer type and name are matched against *.transform*)

  6. Thus system/postscript/pc-win/hp.color.laserjet.transform is selected.

Examples

There are two example sources that script authors may find useful as starting points or reference:

    [install-path]/providers/print/[platform]/transforms/examples
    [install-path]/providers/print/[platform]/transforms/system
                

Important

Transforms in the system directory are used by the PaperCut Global Print Driver. They are system provided. You should not place your own scripts in the system directory. Your own scripts should be in the custom directory. Any changes made in the system directory will be overwritten in an upgrade.

Transform Language Functions & Specification

CommandDescription

var = expression

Evaluate the expression and assign the variable var with the result.

IF condition THEN statement

Evaluate the condition expression, and if true execute the statement.

FIND pattern [options]

Find the pattern in the spool file, and assign $0, $1, ... with the regular expression capture group.

FIND pattern REPLACE text [options]

FIND as above, then replace the string matched by the pattern with text.

STRIP_HEADER

Strip any PJL, XPIF, PostScript or other header in the spool file.

DELETE_UNTIL text

Delete from the start of the spool file up to but not including the first occurrence of text.

INSERT ofs len text

Insert the string text at the spool file offset ofs, after deleting len bytes.

DELETE ofs, len

Delete len bytes from the spool file, starting at the offset ofs.

Table E.1. PDL transform command functions

Assignment

var = expression

e.g. x = 1

Evaluate the expression and assign the variable var with the result. If the expression contains any $[N] and/or %variable% tokens, they are replaced with their current values. To prevent variable substitution, include __no_replace__ in the variable name e.g. __no_replace__template.

IF THEN

IF condition THEN statement

e.g.

    IF duplex THEN pjl_duplex = "ON"
                    

Evaluate the condition expression, and if true execute the statement.

Rules for evaluating expressions

  1. A number x is true if x != 0.

  2. A string pattern is true if it can be found in the spool file using the rules in the FIND pattern [options] below. Strings can be regular expressions or plain strings, and have two optional attributes FIRST | LAST and a search distance. FIRST | LAST does not affect logical evaluation. Search distance does. e.g.

        /<<.*?\/ProcessColorModel\s*\/(DeviceCMYK|DeviceGray).*?>>\s*setpagedevice/ 10000
                                   

    will be true if this regular expression is matched in the first 10,000 bytes of the spool file.

  3. Numbers can be compared with ==, !=, <, >, <= and >=.

  4. Strings can be compared with == and !=. These comparisons are case insensitive and do not perform the searches in rule 2 above.

  5. Logical expressions, such as the results of 1-4 above, can be combined with NOT, AND, OR, XOR, and (...) parentheses. e.g. x == 1 AND NOT (y > 2 OR z <= 3)

FIND

FIND pattern [options]

where the pattern is a regular expression (regex) or string.

FIND /regex/ [REPLACE text] [options]

FIND "string" [REPLACE text] [options]

FIND searches for the pattern (a string or a regex) in the spool file and assigns $0, $1, ... from the resulting regular expression capture groups. If the pattern is a string, then only $0 is assigned.

e.g

    FIND /<<.*?\/ProcessColorModel\s*\/(DeviceCMYK|DeviceGray).*?>>\s*setpagedevice/
                   

could set $0 to "<< /ProcessColorModel /DeviceCMYK >> setpagedevice" and $1 to "DeviceCMYK" on a match.

Options

  • FIRST: Return the first match in the spool file. This is the default

  • LAST: Return the last match in the spool file.

  • n: Any positive integer. Search n bytes of the spool file. The default is to search one megabyte. A value of zero (0) will search through the entire spool file.

FIND REPLACE

FIND pattern REPLACE text [options]

where the pattern is a regular expression (regex) or string.

e.g

     FIND "Letter" REPLACE "A4"
     FIND /(\w+)\s=\sGrayscale/ REPLACE "$1 = BlackAndWhite"
     FIND /MODE = \w+/ REPLACE "MODE = %my_var%"
     FIND /MODE = \w+/ REPLACE "MODE = %my_var%" 2000
                    

The FIND works as described above. Then REPLACE substitutes all the $[N] and %variable% values in the text, before replacing the string matched in the spool file with the substituted text.

ADD_HEADER

ADD_HEADER text

e.g.

    ADD_HEADER my_header
                    

Insert the string text as a header in the spool file.

STRIP_HEADER

STRIP_HEADER

Strip any PJL, XPIF, PostScript or other header (that our developers know about) from the spool file.

DELETE_UNTIL

DELETE_UNTIL text

e.g

    DELETE_UNTIL "%!PS-Adobe-3.0"
                    

Delete from the start of the spool file up to but not including the first occurrence of text.

INSERT

INSERT ofs len text

e.g

    INSERT regex_ofs regex_len my_replacement
                    

Insert the string text at the spool file offset ofs, after deleting len bytes.

DELETE

DELETE ofs len

e.g

    DELETE regex_ofs regex_len
                    

Delete len bytes from the spool file, starting at offset ofs.

It is equivalent to:

INSERT ofs len ""

Pre-Populated Variables

VariableDescriptionExampleType

pc_pages

Number of pages in the spool file

11

int

pc_page_width

Page width in mm

210

int

pc_page_height

Page height in mm

297

int

pc_paper_name

Paper size name

"A4"

string

pc_grayscale

Is the document grayscale?

True

boolean

pc_duplex

Is the document duplex?

False

boolean

pc_tumble

Is the back side of a duplex job rotatated 180 degrees?

False

boolean

pc_docname

Name of the document

"Homework.doc"

string

pc_user

Name of the user

"Josh"

string

pc_server

Print server name

"Server1"

string

pc_printer

Printer name

"Hall printer"

string

pc_driver

Name of the printer driver

"HP Color LaserJet CM4540 MFP PCL 6 (0.3.1545.9108)"

string

pc_iso_date

Current date in ISO format

"2014-08-15"

string

pc_uid

A randomly generated ID

"580459f0-2d19-11e4-b70a-f8b156c33bc3"

string

pc_docname__clean__

'Cleaned' version of pc_docname. All character that will prevent display in PostScript, PJL or XML removed.

"Homework.doc"

string

pc_user__clean__

'Cleaned' version of pc_user.

"Josh"

string

Table E.2. Pre-populated PDL transform script variables

Test Mode

Test mode is designed to accelerate the development, testing and debugging of transform scripts. Test mode is enabled by adding the following line to a transform script:

    ENABLE_TEST_MODE
                

or by setting

    EnableTransformTestMode=yes
                

in the print-provider.conf file. The test mode option should only be enabled while developing scripts.

Test mode causes the system to output additional log files to assist in developing and validating transforms. These files are located at:

    [install-path]/providers/print/[platform]/transforms/logs/
	            

The test mode files created are:

[job-id].log

This file contains logging information to help you understand the transform script’s state and variables.

[job-id].before

The print job spool file BEFORE transformation.

[job-id].after

The print job spool file AFTER transformation.

Table E.3. PDL transform test mode output files

Tip

Consider using a "visual diff" program to help compare before and after files.

Important

Always disable test mode after developing your transform script. Test mode adds a considerable performance overhead and should not be used in a production environment.

Tips & Tricks

  • Develop your scripts in TEST_MODE to help compare script behavior.

  • Use existing examples as starting points.

  • Print the same documents from source and destination printer drivers, and diff the resulting spool files. In most cases the things you will need to modify are in the diff. e.g. One file has a header and the other does not, or one file sets color/grayscale with one string and the other file uses a different string.

  • Look at a PostScript Printer Description (PPD) file of the destination printer, and copy PostScript snippets into a transform.