gperl — groff preprocessor for Perl parts in roff files


gperl [-] [--] [ filespec …]

gperl -h|--help
gperl -v|--version


This is a preprocesor for groff(1). It allows to add perl(7) code into groff(7) files. The result of a Perl part can be stored in groff strings or numerical registers based on the arguments at a final line of a Perl part.


So far, there are only filespec or breaking options.

filespec are file names or the minus character - character for standard input. As usual, the argument -- can be used in order to let all fowllowing arguments mean file names, even if the names begin with a minus character -.

An option is breaking, when the program just writes the information that was asked for and then stops. All other arguments will be ignored by that. These breaking options are heree

-h | --help

Print help information with a short explanation of options to standard output.

-v | --version

Print version information to standard output.

Perl Parts

Perl parts in groff files are enclosed by two .Perl requests with different arguments, a starting and an ending command.

Starting Perl Mode

The starting Perl request can either be without arguments, or by a request that has the term start as its only argument.

  • .Perl
  • .Perl start

Ending Perl Mode without Storage

A .Perl command line with an argument different from start finishes a running Perl part. Of course, it would be reasonable to add the argument stop; that's possible, but not necessary.

  • .Perl stop
  • .Perl other_than_start

The argument other_than_start can additionally be used as a groff string variable name for storage — see next section.

Ending Perl Mode with Storage

A useful feature of gperl is to store one or more results from the Perl mode.

The output of a Perl part can be got with backticks `...`.

This program collects all printing to STDOUT (normal standard output) by the Perl print program. This pseudo-printing output can have several lines, due to printed line breaks with \n. By that, the output of a Perl run should be stored into a Perl array, with a single line for each array member.

This Perl array output can be stored by gperl in either

groff strings

by creating a groff command .ds

groff number register

by creating a groff command .rn

The storage modes can be determined by arguments of a final stopping .Perl command. Each argument .ds changes the mode into groff string and .nr changes the mode into groff number register for all following output parts.

By default, all output is saved as strings, so .ds is not really needed before the first .nr command. That suits to groff(7), because every output can be saved as groff string, but the number registers can be very restrictive.

In string mode, gperl generates a groff string storage line

.ds var_name content

In number register mode the following groff command is generated

.nr var_name content

We present argument collections in the following. You can add as first argument for all stop. We omit this additional element.

.Perl .ds var_name

This will store 1 output line into the groff string named var_name by the automatically created command

.ds var_name output
.Perl var_name

If var_name is different from start this is equivalent to the former command, because the string mode is string with .ds command. default.

.Perl var_name1 var_name2

This will store 2 output lines into groff string names var_name1 and var_name2, because the default mode .ds is active, such that no .ds argument is needed. Of course, this is equivalent to

.Perl .ds var_name1 var_name2


.Perl .ds var_name1 .ds var_name2
.Perl .nr var_name1 varname2

stores both variables as number register variables. gperl generates

.nr var_name1 output_line1
.nr var_name2 output_line2
.Perl .nr var_name1 .ds var_name2

stores the 1st argument as number register and the second as string by

.nr var_name1 output_line1
.ds var_name2 output_line2

Printing towards STDERR is without Storage

The printing towards STDERR, (standard error) works as usual. All error information goes to the real normal standard error, without other automatical storage.


A possible Perl part in a roff file could look like that:

.Perl start
my $result = 'some data';
print $result;
.Perl stop .ds string_var

This stores the result ”some data” into the roff string called string_var, such that the following line is printed:

.ds string_var some data

by gperl as food for the coming groff run.

A Perl part with several outputs is:

.Perl start
print ”first\n”;
print ”second line\n”;
print ”3\n”;
.Perl var1 var2 .nr var3 

This stores 3 printed lines into 3 groff strings. var1,var2,var3. So the following groff command lines are created:

.ds var1 first
.ds var2 second line
.nr var3 3

See Also

Man-pages related to groff are groff(1), groff(7), grog(1), and groffer(1).

Documents related to Perl are perl(1), perl(7).


Copyright © 2014 Free Software Foundation, Inc.

This file is part of gperl, which is part of groff, a free software project. You can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.

The license text is available in the internet at


This file was written by Bernd Warken.


4 November 2014 Groff Version 1.22.3