running a script from cron every second

Question

i have a script which i am running from browser with meta refresh and it workd without any issue in browser but it will not work in cron so what i can do to run every second from cron? i know with sleep i can but i have to create several cron tab in cron job and every time i have to run the script

with sleep how can i run this script every 5 sec.

<meta http-equiv="refresh" content="5;url=test.php">
<?php
    $res = mysql_query("SELECT * FROM tableA where st='0' order by id asc LIMIT 1");
    $row = mysql_fetch_array($res);

    $link= $row['wl'];

    function getTitle($Url){
        $str = file_get_contents($Url);
        if(strlen($str)>0){
        preg_match("/\<\/td\><\/tr\><tr\><td colspan\=2\>(.*)\<\/td\>/",$str,$title);

            return $title[1];
        }
    }
    getTitle($link);
?>

You know the mysql_* functions are deprecated, don't you?

Marcel Korpel
– Marcel Korpel

2013-10-26 11:29:33 +00:00
Commented Oct 26, 2013 at 11:29 — Marcel Korpel
– Marcel Korpel, Commented Oct 26, 2013 at 11:29

sectus · Accepted Answer · 2013-10-26 11:49:20Z

9

Just add to your crontab

* * * * * for i in {0..59}; do curl http://your.domain.zone/page.html && sleep 1; done;

for added because cron could not run faster than once per minute.

edited Oct 26, 2013 at 11:49

answered Oct 26, 2013 at 11:29

sectus

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16 Comments

user2761874 Over a year ago

how cron will know that when it has to be run

sectus Over a year ago

@user2761874, it knows because it's a scheduler.

user2761874 Over a year ago

getting error "-":21: bad command errors in crontab file, can't install.

Marcel Korpel Over a year ago

This will cause a lag-behind: the execution of the script will take some time, then execution sleeps for 1 second, and so on; after 59 iterations you'll notice that total execution time might be longer than 1 minute, causing the script being executed twice within a near distance.

sectus Over a year ago

@MarcelKorpel, you are right. It must to be a async calling with curl.

|

jancha · Accepted Answer · 2013-10-26 12:06:33Z

1

Minimum call interval is 1 minute for cron

If you need more frequent calls, you have multiple choices:

Create a daemon which is launched and then inside daemon you can put your own checks/sleep etc.
You can listen to file system events to trigger processing of whatever tasks you need
You can still use meta/js to "reload" page with combination of cron, but in that case you need to use headless browser such as phantomjs to handle your page and reloads properly. So you would be opening your "page" once a minute, and page would do 60/5=12 reloads itself using either js or meta tag.

clearly 3 is the worst. normally you would go either with option (1) or (2), depending on your system requirements.

answered Oct 26, 2013 at 12:06

jancha

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