This is a preprocessor for groff(1). It allows the use of perl(7)
code in 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 following 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 here
-h | --help
Print help information with a short explanation of options to
-v | --version
Print version information to standard output.
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 startEnding 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
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
by creating a groff command .dsgroff 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
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
.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
.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
.nr var_name1 output_line1.ds var_name2 output_line2Printing 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 automatic storage.
A possible Perl part in a roff file could look like that:
my $result = 'some data';
.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:
print ”second line\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
This page is part of the groff (GNU troff) project. Information
about the project can be found at
⟨http://www.gnu.org/software/groff/⟩. If you have a bug report for
this manual page, see ⟨http://www.gnu.org/software/groff/⟩. This
page was obtained from the project's upstream Git repository
⟨https://git.savannah.gnu.org/git/groff.git⟩ on 2020-07-14. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-07-12.) If you discover any rendering problems in
this HTML version of the page, or you believe there is a better or
more up-to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not part
of the original manual page), send a mail to firstname.lastname@example.org
groff 220.127.116.11-3ba6 16 May 2020 gperl(1)