Friday, 13 July 2007

$* replacement

So, the special variable $* has been removed from perl 5.10, after having been deprecated for years. For those who don't remember Perl4-style programming, $* was used to enable multi-line matching in regular expressions. In Perl 5, the preferred way to do it is to use the more flexible regexp flag /m.

I removed that poor old variable not because I like removing old things, but because it was standing in the way of a bug I wanted to fix (bug #22354). Anyway. Apparently there is still out there some old Perl code that fears not using $*. And notably ghc's evil mangler, which broke with perl 5.9.5.

But Audrey Tang (who else?) found an elegant way to emulate $* = 1, in a characteristic perl-zen manner. Here's how: the current evil mangler contains this simple line of code, in a BEGIN block:

require overload; overload::constant( qr => sub { "(?m:$_[1])" } );

Wednesday, 11 July 2007

Saving GNOME settings

Here's a small tip I got from GNOME expert Pascal Terjan, and that I'm copying here because I don't trust my memory:

Want to inspect the settings of some GNOME application? Use gconf-editor.

Want to copy the settings of some GNOME app (like, say, metacity) from one desktop to another? Use the command-line tool gconftool, specifically the options --dump and --load. (The paths you need to feed to gconftool can be retrieved via gconf-editor.)

Tuesday, 10 July 2007

Munin plugin for ping response time

My ADSL router (a freebox) shows a recent tendency to desynchronize itself. That's annoying, even it that only lasts a few minutes from time to time. Maybe a cable needs to be replaced (advice?). So, I quickly hacked this plugin for Munin, an excellent system monitoring package:

#!/usr/bin/perl -wT

use strict;

our @HOSTS = qw(;
if (@ARGV && $ARGV[0] eq 'config') {
print <<CONFIG;
graph_title Ping response time
graph_vlabel time (ms)
graph_args --base 1000 -l 0
graph_scale no
graph_category network
for my $host (@HOSTS) {
my $name = $host;
$name =~ tr/./_/;
print "$name.label $host\n";
else {
@ENV{qw(PATH)} = qw(/bin);
for my $host (@HOSTS) {
my $name = $host;
$name =~ tr/./_/;
my @ping = qx(/bin/ping -nc1 $host 2>/dev/null);
my $times = $ping[-1];
my $val = '';
if ($times =~ m{^rtt min/avg/max/mdev = ([\d.]+)}) {
$val = $1;
print "$name.value $val\n";

Feel free to adapt/improve. This code is of course released under whatever license Munin is released under (I didn't bother to check.)

Monday, 9 July 2007

Perl 5.9.5

I've released Perl 5.9.5 on saturday. Get it while it's hot. Get the official announcement as well.

Wednesday, 4 July 2007


I've released another new heavily magic Perl module on CPAN, this time scratching an itch of Yves Orton. It's called Sub::Current and allows you to get a reference to the currently executing subroutine.

At first I wanted to use a tied scalar instead of a function to get this reference; however, due to the way parameter passing is implemented in Perl, that's not easily possible: the tied variable (let's call it ${^ROUTINE}) is FETCHed at the innermost scope, so this won't work:

sub foo {
# here ${^ROUTINE} points to bar(), not to foo() !
bar( ${^ROUTINE} );

I think that could be done by tweaking some of the ck_ functions that are used to optimize Perl's internal optree during the compilation phase. I know that some people are not afraid to do this, but I feel that this would be a rather fragile solution, for only a little bit of syntactic sugar.