The next script can be usefull to list all PIDs of a given process and its childs (i.e.: threads also under Linux)

It’s quite brute-force, using /proc extensively. Most probably very Linux specific…

#!/usr/bin/perl -w

use strict;

my $pid=shift @ARGV;

# We'll first make a hash %h where:
# each key is the PID of a process
# each value is a list of the PIDs of the sub-process (direct descendant (ie: children) only, no grand child,...)

# we'll loop on all files under /proc, and take only those whose filename is a number
opendir(DIR,"/proc/") or die ("Can't list proc");
my $file;
my %h=(); # key=pid, value=list of children
while($file=readdir(DIR)) {
        next unless $file =~ m/^d+$/;  # only numbers
        open(STAT,"/proc/$file/stat") or next; # open the stat file for this process
        my $s=<STAT>;
        my @f=split(/s+/,$s);
        # pid: $f[0]   parent PID: $f[3]
        push @{ $h{$f[3]} },$f[0];
        close(STAT);
}
closedir(DIR);

my @pids=();

# recursive function to add a pid and the PIDs of children, grand-children,...
sub add($) {
        push @pids,$_[0];
        map { add($_) } @{ $h{$_[0]} } if (defined($h{$_[0]}));
}
# print join("n", map { $_ . ':' . join(',',sort @{ $h{$_}  } )} sort keys %h);

add($pid);

# output results
print join(' ',@pids)."n";

MySQL v4.0 doesn’t handle encoding very well. Basically, its considering everything you send it as simple binary data. At least, it doesn’t corrupt it, but no conversion is made. I had to interact, from Perl, with a database which was populated by PHP (v4 also), and which had ISO-8859-1 data in it.
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I’ve spent a few years writing Perl without ever looking carefully at the map function, but since I’ve discovered it, I use it often. I propose here some sample usage that I’ve found usefull. I’ll also show how to use the grep function, which is quite similar in usage.
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Today, I had to enable a custom program to inject posts in a WordPress blog. Since WordPress implements not less than 3 differents APIs to this effect, through XMLRPC, the choice of the technology was easy: Perl and xmlrpc.

The task was complicated by the fact that the page was only accessible by passing through an HTTP Basic Authentication.

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I’ve tripped on this simple question:
Having a perl hash %h, and knowing that is has only one element, how to get to this element as easily / as efficiently as possible? Of course, we suppose here that you don’t know the key corresponding to this element…
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Yacc, and its GNU replacement Bison is a parser generator, i.e. a program to generate some routines which can parse some text and data according to a user-specified grammar.The basic Yacc documentation is availlable on the net, or with man yacc. We detail here only some points.
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