Unix Cron Not Executing - php

Question

I'm executing a shell script as a cron job every minute like so:
* * * * * /bin/bash /var/www/html/stream.sh
The script contains the following code:
#!/bin/sh
if ps -ef | grep -v grep | grep get_tweets.php ; then
exit 0
else
nohup php /var/www/html/streaming/db/get_tweets.php > /dev/null &
exit 0
fi
I'm also running another shell script as a cron, the only difference between the two is "get_tweets" is replaced with "parse_tweets_keyword" and cron is executed like so:
* * * * * /bin/bash /var/www/html/process-check.sh
Problem is, whilst the latter cron works perfectly fine, the first doesn't seem to run the script successfully, however when I run the command:
nohup php /var/www/html/streaming/db/get_tweets.php > /dev/null &
The script runs perfectly, so i'm not entirely sure what the problem is. The permissions for all files are correct and executable and i'm running the crons as root under crontab and both of the PHP script that i'm attempting to execute are running as background processes.
If anyone can help or knows the issue, would be greatly appreciated. I'm also open to better ways of running the PHP script perhaps as a single line in crontab rather than running the shell script to run the PHP script via cron.

Answer 1

So it seems this was the answer to my question:
#!/bin/sh
cd /var/www/html/streaming/db
if ps ax | grep -v grep | grep get_tweets.php ;
then
exit 0
else
nohup php ./get_tweets.php > /dev/null &
exit 0
fi
It would appear even running as root get_tweets.php would not execute without first changing the directory prior to actually running the command. As per the second line:
cd /var/www/html/streaming/db
Although I'm not entirely sure why it wouldn't run, as parse_tweets_keyword.php ran perfectly using the first bash script posted in my question.