How can I have a bash script create a cron job that runs every 15 minutes?

I want to have a bash script add a cron job that runs a php script every 15 minutes.
I know how to do it using:
export VISUAL=emacs
crontab -e
and then edit it manually.
But how can I automate that in a script?

Also on a sidenote this is the example crontab that the app I am trying to run reccomends:
0,15,30,45 * * * * /usr/bin/php /etc/php.ini /etc/php.d /usr/share/php \ /var/www/html/trellis/core/global/interfaces/event_runner.php

Some of these, like php.ini appear to be config files. Why would any app need config files in a cron job?  Can they even be executed?  That seems awfully confusing right now.
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TintinConnect With a Mentor Commented:
Generically speaking, the way to script adding cronjobs is:

crontab -l >/tmp/crontab
echo "0,15,30,45 * * * * /some/command" >>/tmp/crontab
crontab /tmp/crontab

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tate1615Author Commented:
Thank you very much for your help.  It was very fast, clear, and correct. I appreciate it!
Also what do you make of the second half of the posted question?
Does that make any sense to you?  Why would anyone's lamp web app need a crontab that runs php.ini?  What do you make of it?
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