Using the Inkscape shell from perl - perl

Question

Inkscape has a shell mode invoked like this
inkscape --shell
where you can execute commands like this:
some_svg_file.svg -e some_png_output.png -y 1.0 -b #ffffff -D -d 150
which will generate a PNG file, or like this:
/home/simone/some_text.svg -S
which gives you the bounding box of all elements in the file in the return message like this
svg2,0.72,-12.834,122.67281,12.942
layer1,0.72,-12.834,122.67281,12.942
text2985,0.72,-12.834,122.67281,12.942
tspan2987,0.72,-12.834,122.67281,12.942
The benefit of this is that you can perform operations on SVG files without having to restart Inkscape every time.
I would like to do something like this:
sub do_inkscape {
my ($file, $commands) = #_;
# capture output
return $output
}
Things work OK if I use open2 and forking like this:
use IPC::Open2;
$pid = open2(\*CHLD_OUT, \*CHLD_IN, 'inkscape --shell');
$\ = "\n"; $/ = ">";
my $out; open my $fh, '>', \$out;
if (!defined($kidpid = fork())) {
die "cannot fork: $!";
} elsif ($kidpid == 0) {
while (<>) { print CHLD_IN $_; }
} else {
while (<CHLD_OUT>) { chop; s/\s*$//gmi; print "\"$_\""; }
waitpid($kidpid, 0);
}
but I can't find out how to input only one line, and capture only that output without having to restart Inkscape every time.
Thanks
Simone

Answer 1

You don't need to fork, open2 handles that by itself. What you need to do is find a way of detecting when inkscape is waiting for input.
Here's a very basic example of how you could achieve that:
#! /usr/bin/perl
use strict;
use warnings;
use IPC::Open2;
sub read_until_prompt($) {
my ($fh) = (#_);
my $done = 0;
while (!$done) {
my $in;
read($fh, $in, 1);
if ($in eq '>') {
$done = 1;
} else {
print $in;
}
}
}
my ($is_in, $is_out);
my $pid = open2($is_out, $is_in, 'inkscape --shell');
read_until_prompt($is_out);
print "ready\n";
print $is_in "test.svg -S\n";
read_until_prompt($is_out);
print $is_in "quit\n";
waitpid $pid, 0;
print "done!\n";
The read_until_prompt reads from inkscapes output until it finds a > character, and assumes that when it sees one, inkscape is ready.
Note: This is too simple, you will probably need more logic in there to make it work more reliably if a > can appear outside the prompt in the output you're expecting. There is also no error checking at all in the above script, which is bad.