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gperl

Section: User Commands (1)
Updated: 2 July 2023
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Name

gperl - execute Perl commands in groff documents
.nr d-fallback 1
.nr d-fallback 1

Synopsis

[file~...] -h --help -v --version

Description

This is a preprocessor for It allows the use of code in 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 [lq]-[rq], gperl reads the standard input stream. A doubl-dash argument ([lq]--[rq]) 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 [ga]...[ga]. This program collects all printing to STDOUT (normal standard output) by the Perl print program. This pseud-printing output can have several lines, due to printed line breaks with rsn. 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 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 = [aq]some data[aq]; print $result; .Perl stop .ds string_var after

This stores the result rqsome datarq 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 rqfirstrsnrq; print rqsecond linersnrq; print rq3rsnrq; .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

Authors

gperl was written by Bernd Warken

Example

Authors

See also