Calling lockf from the shell line works fine, but in the script, it fails

Overworked_PhD · 04-12-2009, 11:29 AM

Everything seems to work fine when I do the following...

Code:

% lockf -t 30 /usr/party/log/party.log sleep 30

Now when I add it to a perl script like in the following

Code:

#!/usr/bin/perl
use warnings;

my $value;
while (True)
{
    if(`w | grep cd | grep party`) {
        `lockf -t 30 /usr/party/log/party.log sleep 30`;
        sleep(30);
    }
    else {
        print "not logged in\n";
    }
    sleep(1);

}

It doesn't work even though lockf shows up on my ps table.

Quote:

cdalten 50123 0.0 0.2 3764 2580 pl IN 12:51PM 0:00.32 -zsh (zsh)
cdalten 52997 0.0 0.2 2796 2276 pl SN+ 1:30PM 0:00.05 /usr/bin/perl ./scan.pl (perl5.8.8)
cdalten 53078 0.0 0.1 1256 596 pl SN+ 1:31PM 0:00.00 lockf -t 30 /usr/party/log/party.log sleep 30
cdalten 53079 0.0 0.0 1256 432 pl SN+ 1:31PM 0:00.00 sleep 30

I don't get why it fails when I run it in a perl script.

MK27 · 04-12-2009, 11:50 AM

It seems silly to me to use a perl script just to issue shell commands; why don't you put them in a shell script?

To lock a file in perl use flock().

Overworked_PhD · 04-12-2009, 11:58 AM

Quote:

Originally Posted by MK27

It seems silly to me to use a perl script just to issue shell commands; why don't you put them in a shell script?

To lock a file in perl use flock().

I'd still get the same results and hence it wouldn't solve my current problem.

MK27 · 04-12-2009, 01:02 PM

Quote:

Originally Posted by Overworked_PhD

I'd still get the same results and hence it wouldn't solve my current problem.

are you saying that this

Code:

#!/bin/bash

lockf -t 30 /usr/party/log/party.log sleep 30

will not execute EXACTLY as if you had typed it into the command-line? Because I don't believe you!

I do not have a "lockf" command on my system, so I can't help you with the syntax*, but shell scripts are executed by the shell one line at a time. If it works on the command line, it will work in a shell script. Here:

Code:

!/bin/bash

if grep "bash" | grep "cdalten" > /dev/null
    then lockf -t 30 /usr/party/log/party.log sleep 30
    else echo "not logged in"
fi

The purpose of "> /dev/null" is to spare you the grep output on screen.

*eg, I'm assuming "sleep 30" at the end is a parameter and not a typo for "&& sleep 30"

Overworked_PhD · 04-12-2009, 03:28 PM

Your script only works after I press ctrl-c. I'm assuming the process is doing some kind of forking that I'm not aware of.

MK27 · 04-13-2009, 09:55 AM

Quote:

Originally Posted by Overworked_PhD

Your script only works after I press ctrl-c. I'm assuming the process is doing some kind of forking that I'm not aware of.

Code:

cat textfile | thatscript.sh
or
thatscript.sh < textfile

Sorry, it was intended to process input, I thought that was clear.

04-12-2009, 11:50 AM	#2
MK27 critical genius Join Date: Jul 2008 Location: SE Queens Posts: 5,207	It seems silly to me to use a perl script just to issue shell commands; why don't you put them in a shell script? To lock a file in perl use flock(). __________________ "A man can't just sit around." -- Larry Walters
MK27 is online now

04-12-2009, 03:28 PM	#5
Overworked_PhD Registered User Join Date: May 2007 Location: Berkeley, CA Posts: 140	Your script only works after I press ctrl-c. I'm assuming the process is doing some kind of forking that I'm not aware of.
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