how to set cron job from php script?

Question

i am new to cron job . i studied some basics about cron job . i can able to call php using cron tab. By using following command in /etc/crontab

  10 *    * * *   root    /usr/bin/php /var/www/PATH TO SCRIPT/email.php 

In email.php i have following code

 #!/usr/bin/php
 <?php
    mail ("[email protected]", "Cron Successful Public HTML!","Hello World from mycron.php!");
 ?>

For every 10mins i am getting mail. But i need to know is there any way to call cron job from php ( invoke cron from php) i get some idea by surfing but i am not able to figure out the exact way to do my job . Here is code which i used to add job by using php

   exec('echo -e "crontab -e \n2 * * * * /usr/bin/php /var/www/PATH TO THE SCRIPT/crontest1.php" ');

Its not working for me. can anyone please guide me how to call or add cron from php. so tat i can send mail by executing php file & can able change time interval in php file itself.

Solution

From How can I set cron job through PHP script by Nick Clark:

This will add a script that runs every day at 9:30am.

exec('echo -e "`crontab -l`\n30 9 * * * /path/to/script" | crontab -');

You may run into problems with permissions if you are running this script from a web server. To get around this, I would suggest a different approach.

Here is one possible solution. Create a list of scripts that need to be run. You can save this in a text file or in a database. Create a script to read this list and run it every minute or every 5 minutes (using a cronjob). Your script will need to be smart enough to decide when to run the list of scripts and when to simply exit.

You can do like this..

Other links:

Install a cron job with a php script

How to invoke cron job from php script?