Ubuntu Manpage: gperl - execute Perl commands in groff documents

Name

       gperl - execute Perl commands in groff documents

Synopsis

       gperl [file ...]

       gperl -h
       gperl --help

       gperl -v
       gperl --version

Description

       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.

       If  no  operands  are  given, or if file is “-”, gperl reads the standard input stream.  A
       double-dash argument (“--”) causes all subsequent arguments  to  be  interpreted  as  file
       operands,  even  if their names start with a dash.  -h and --help display a usage message,
       whereas -v and --version display version information; all exit afterward.

Perl regions

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 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
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 registers can be very restrictive.

In string mode, gperl generates a groff string storage line
.ds var_name content
In 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
and
.Perl .ds var_name1 .ds var_name2

.Perl .nr var_name1 varname2
stores both variables as 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 register and the second as string by
.nr var_name1 output_line1
.ds var_name2 output_line2

Example

       A possible Perl part in a roff file could look like that:
              before
              .Perl start
              my $result = 'some data';
              print $result;
              .Perl stop .ds string_var
              after

       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

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