Perl: What does this construct mean?

Team Member Joined: 09 Jan 2002 Posts: 147 Location: UK

What does the $< mean in the following code? I'm no expert at Perl but I'm trying to understand how the code, of which this is a part, works.

Code:

#!/usr/local/bin/perl

# restart

if ($< == 0) {
$usr = $ARGV[0];
} else {
$usr = (getpwuid($<))[0];
}

Posted: Mon Jul 08, 2002 6:03 am (21 years, 9 months ago)

Peter wrote:

What does the $< mean in the following code? I'm no expert at Perl but I'm trying to understand how the code, of which this is a part, works.

Code:

#!/usr/local/bin/perl

# restart

if ($< == 0) {
$usr = $ARGV[0];
} else {
$usr = (getpwuid($<))[0];
}

Is the Effective UID for the perl script.
Check to print this in a script like
print " UID = $< "\n;

$> can be use for setting the UID of the script like:
$> = 2000;

Team Member Joined: 09 Jan 2002 Posts: 147 Location: UK

Thanks Jos. You see, I have the following script on my server called restart_apache, which I run whenever I want to restart apache:

Code:

#!/usr/local/bin/perl

# restart

if ($< == 0) {
$usr = $ARGV[0];
} else {
$usr = (getpwuid($<))[0];
}

print "Restarting apache for $usr ...\n";

$pscmd = "ps -auxww";

open(PS, "$pscmd|") || die "can't run $pscmd: $!";

$title = <PS>; # eat the title off ps

while($cand = <PS>) {
chop($cand);
($user, $pid, $pcpu, $pmem, $vsz, $rss, $tt, $stat, $started, $time, $command)
= split(' ', $cand);

if ($user eq $usr && ($command =~ /http/ || $command =~ /^Master:/ || $command =~ /^Child:/) ) {
`kill $pid`;
}

}

I've been trying to run this script via an exec call in a PHP web page (I'm attempting to build a nice web-based control panel for my server) and the script gets as far as printing "Restarting apache for reywob" and then it doesn't appear to get any further, as the "kill xxxx" commands don't get printed to the output.

Any ideas?
Thanks

WebHelper Joined: 01 Mar 2003 Posts: 69 Location: Texas

Peter wrote:

I've been trying to run this script via an exec call in a PHP web page (I'm attempting to build a nice web-based control panel for my server) and the script gets as far as printing "Restarting apache for reywob" and then it doesn't appear to get any further, as the "kill xxxx" commands don't get printed to the output.

Any ideas?

Okay, I realize that this is a really old post...

Did you consider that once you restart apache your session isn't valid any more? How are you going to get communications back to a web page when the system responsible for serving that data (apache) isn't there?

Or am I just confused about what you're trying to do. Or - since this post is ages old anyway - who cares... Rolling Eyes

Dave

Team Member Joined: 09 Jan 2002 Posts: 147 Location: UK

drathbun wrote:

Okay, I realize that this is a really old post...

Did you consider that once you restart apache your session isn't valid any more? How are you going to get communications back to a web page when the system responsible for serving that data (apache) isn't there?

Nope, I forgot all about that Shocked

Anyhow, I've moved off that server now, so whether it's possible or not doesn't matter any more - but thanks for pointing it out, I'm glad to have learned why it wouldn't work!

Peter

WebHelper Joined: 01 Mar 2003 Posts: 69 Location: Texas

Peter wrote:

Nope, I forgot all about that Shocked

It's alwalys the simple things that bite you... Laughing

Dave