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Re: [MacPerl-Scribes] "Basic Perl Filters in BBEdit" Column
Larry Moore, said in Re: [MacPerl-Scribes] "Basic Perl Filters in BBEdit"
Column at Apr/20/2000, Thu 06:52:34.
> Minutes of "Basic Perl Filters in BBEdit" Column as/at 10 April
[snip]
Okay, I'm more or less back. Things did not go well yesterday, and I'm
more or less in the same position regarding the status of my Mac, albeit
with a slightly faster modem in place.
Although I applaud Larry's efforts, His HTML is questionable. He's also
missing the comments I got from Jim Corriea yesterday off list (happened
too late last night to bother posting it here).
So, here's what I've got NOW, and believe me some of whats been said, has
helped.
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"
"http://www.w3.org/TR/REC-html40/loose.dtd">
<html>
<head>
<title>Perl Filters in BBEdit</title>
<meta name="generator" content="BBEdit 5.1.1">
</head>
<body bgcolor="#ffffff">
<h2>Basic Perl Filters in BBEdit</h2>
<p>
Back in issue #7, Vicki Brown wrote about her "<a
href="http://www.perlmonth.com/columns/mac_perl/mac_perl.html?issue=7">MacPe
rl Development Environment</a>". For the most part, what she
describes there is a typical setup for a serious MacPerler. In her article
Vicki covered, among other things, BBEdit, from <a
href="http://www.barebones.com/">Bare Bones Software</a>. As of version
5.1, BBEdit has MacPerl support built in. Older versions used a plug-in
module for roughly the same functionality. However having built-in support
means MORE than just the ability to use BBEdit as a text-editor and front
end for MacPerl.
</p>
<p>
BBEdit allows you to create "Perl Filters": scripts to which a
text selection, or even an entire document may be passed, which then return
their results to BBEdit. BBEdit isn't the only Mac text-editor with
built-in Perl support, and neither is it the only such editor which lets
you use Perl scripts as text filters. <a
href="http://alpha.olm.net/">Alpha</a> has similar functionality and a very
vocal following. I'm hoping to corral one of those vocal followers into
writing a column on the subject.
</p>
<p>
I spoke (via email) with Jim Correia, Senior Software Engineer at Bare
Bones Software. Although perl filters weren't his idea (credit rightly
goes to Brad Hanson for that), he did do a complete rewrite of the code for
BBEdit 5.1. It's safe to say that Jim's intimately familiar with the code.
I asked Jim to describe what a Perl Filter does:
</p>
<blockquote>
A perl filter is a perl program that transforms the selection in an active
BBEdit window. The program takes input as a file path on the command line,
and writes its output to STDOUT. If we were on a unix-like operating
system, the program might be invoked liked this
</blockquote>
<blockquote>
<code>perl filter.plx /usr/tmp/bbedit_selection.txt</code>
</blockquote>
<blockquote>
On the Macintosh, there isn't a command line. Instead BBEdit writes out
the selection to a temporary file called [DocumentName].§ then sends
an apple event to the MacPerl application giving it the program to execute,
the command line parameters (the data file) and sets up some flags telling
MacPerl it should return STDOUT and STDERR in the apple event reply.
BBEdit replaces the selection in the active window with the contents of
STDOUT.
</blockquote>
<blockquote>
So for instance, if I had a window opened called "Testing Perl
Filters" and ran the following perl filter:
</blockquote>
<blockquote>
<pre>
#!perl -w
use strict;
print "$ARGV[0]\n";
</pre>
</blockquote>
<blockquote>
the selection would be replaced with
</blockquote>
<blockquote>
<pre>
Boot:Temporary Items:Testing Perl Filters.§
</pre>
</blockquote>
<blockquote>
More interesting is when we actually have some useful transformation we
want to perform on the data. One such example would be sorting the lines
in a data file:
</blockquote>
<blockquote>
<pre>
#!perl -w
use strict;
my @lines = <>;
@lines = sort @lines;
foreach(@lines){
print;
}
</pre>
</blockquote>
<blockquote>
You can use all of the command line flags in a perl filter that MacPerl
would normally understand. Taking advantage of this, a filter which
reverses all of the characters in each line becomes the canonical perl one
liner:
</blockquote>
<blockquote>
<pre>
#!perl -wpl
$_ = reverse;
</pre>
</blockquote>
<h3>An Example One-Line Filter</h3>
<p>
For the most part, Perl Filters tend to be short (one or two line) scripts,
which do various regular expression functions not possible with BBEdit's
own regex capability. Frequently, you need to make multiple passes over a
document, or parse it in a way which isn't possible with regex alone, like
so:
</p>
<pre>
#!perl -p
s/(\d+)-(\d+)/$1 > $2 ? "$1-$2" : join ', ', $1 .. $2/ge
</pre>
<p>
Alas, I'm not the author of this gem. This came about as the result of one
of the frequent filter-generation sessions on the BBEdit-Talk[<a
href="#talk-list">1</a>] list. On a Friday, someone blithely asked for a
script which could parse a certain set of strictly formatted strings of
numbers. The problem was first approached using a rather convoluted
AppleScript, which even the author concluded was ugly. Next, a Perler
tried his hand. Finally, Ronald Kimball stepped in, reducing the Perl
script to its most idiomatically concise form. Ron claims the result is
again "ugly", but the original poster referred to it as "inspirational".
</p>
<p>
Oh, and what does it do? The answer is <a
href="http://search.barebones.com/action.lasso?-database=lists.fp3&-
layout=import&-response=%2ftalk%5flists%2fdetail.html&-recid=47440&-
search">here</a>.
</p>
<h3>Filters using Perl Modules</h3>
<p>
Are you lazy? You just don't want to open your mail client to post mail?
You'd rather stay in your text-editor? Well, so did Rory Campbell-Lange:
</p>
<pre>
#!perl -w
# campbell-lange@easynet.co.uk (Rory Campbell-Lange)
# only barely modified from the example in
# the Mail::Send POD
require Mail::Send;
@allmail = <>;
$to = shift @allmail;
chomp $to;
$subject = shift @allmail;
chomp $subject;
$msg = new Mail::Send;
$msg->to($to);
$msg->subject($subject);
$fh = $msg->open;
print $fh "@allmail";
$fh->close;
</pre>
<p>
Oh, but that doesn't handle MIME attachments you say?
</p>
<pre>
#!perl -w
# campbell-lange@easynet.co.uk (Rory Campbell-Lange)
# only barely modified from the example in
# the MIME::Lite POD
use MIME::Lite;
MIME::Lite->send('smtp', "mymail.example.org", Timeout=>200);
my $to = shift;
my $sub = shift;
my $filetoattach = shift;
my $filename = shift;
my @message = @_;
$msg = new MIME::Lite
From =>'me@mymail.co.uk',
To => $to,
#Cc => couldbeshift,
Subject => $sub,
Type =>'TEXT',
Data => @message,
attach $msg
Type =>'image/gif',
Path => $filetoattch,
Encoding => 'base64',
Filename => $filename;
$msg->send;
</pre>
<p>
A sufficiently intrepid programmer could easily use this as the starting
point for a complete mail client, written as a BBEdit Perl Filter!
</p>
<h3>Filters with No Input</h3>
<p>
Nothing says that a "filter" has to take an input to produce an output.
This example creates a timestamp:
</p>
<pre>
#!perl
my ( $year, $month, $day, $hour, $min, $sec) = reverse((localtime)[0 ..
5]);
printf('%04d:%02d:%02d
%02d:%02d:%02d',$year+1900,$month+1,$day,$hour,$min,$sec);
</pre>
<p>
I've done other scripts which do more complex things, such as generating an
XML file, then parsing it to create HTML[<a href="#mother-of-perl">2</a>].
However, I'm saving the really tricky Perl Filters for Chris Nandor.
</p>
<p>
Finally, a word about switches. I've seen more than my share of Perl
Filters, and a lot of evidence that MacPerler's in general are unaware of
which #! switches work under MacPerl, and when and how to use them. This
is really a topic for an entirely separate column, but I'll try to deal
with it briefly here. Most switches work with MacPerl. Of those which
might be considered most useful in the context of Perl Filters:
</p>
<pre>
-n (iterate entire script using <>) works as expected
-p (iterate entire script using <> printing each line) works as expected
-l (automatically chomp line endings from input
-- with -n or -p no terminating \n needed on output) works as expected
-e (execute following string as command-line) generates error message
-- not emulated. Works only under MPW Perl.
-0 (sets $\ in octal) works as expected
</pre>
<p>
Although in this context, I can't imagine you doing such a thing, I feel
the need to point out that:
</p>
<p>
-u (does core dump) Believe me, you don't want to use "-u" on a Macintosh.
</p>
<h3>Next Issue</3>
<h3>References/Footnotes</h3>
<p>
<a name="talk-list">1) BBEdit-Talk Mailing List:</a> <<a
href="mailto:bbedit-talk@barebones.com">bbedit-talk@barebones.com</a>>
To subscribe, visit the Bare Bones Software Web site.
</p>
<p>
<a name="mother-of-perl">2) Mother of Perl</a> <a
href="http://webreference.com/perl/scripts/">http://webreference.com/perl/sc
ripts/</a>, which is actually <b>rewritten</b> there as a BBEdit Include
file. Most of the code is Jonathan Eisenzopf's not mine, I merely had to
figure out new ways of passing data to it.
</p>
</body>
</html>
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