shell_exec and git pull

I was hoping someone could help, I have a PHP page which uses shell_exec to zip up a directory and run git pull to bring down recent repository changes.

$op = shell_exec("cd /home/user/git/$repo/$dir/; zip -r /home/user/archives/$dir.$datestamp.zip $dir; cd /home/user/git/$repo/$dir/; git pull");

The zip works fine. If I change git pull to for example git log or git status - within my shell_exec, this works also, and I can see the log file.

Just doesn't seem to like git pull.

I saw another similar post to this, but wasn't sure how it was achieved >> Shell_exec with git pull?

From your description in the comments it seems that the problem is that your apache user cannot write to the repository, which is clearly required when you use git pull. You have two courses of action:

Setup up Apache to run the script as another user (e.g. using suEXEC either on a VirtualHost or via userdir)
Change the permissions on your repository so the apache user can write to it

You should think carefully about the security implications of either choice, but the second option is probably easiest. If you don't already have such a group, you can create it with:

addgroup gitwriters

... and then add yourself and the Apache user to this group:

adduser [yourusername] gitwriters
adduser apache gitwriters

Then you can follow the instructions in another question to change the permissions on the repository. To reiterate those with some slight variations:

# Recursively, set the group ownership of every file and directory of your repository:
chgrp -R gitwriters /path/to/your/repo

# Recursively, make every file and directory of your repository readable and writable
# by the group:
chmod -R g+rw /path/to/your/repo

# Recursively, set the setgid of every directory in the repository.  The setgid bit
# on directories means that files created in the directory will have the same group
# ownership as the directory.  
find /path/to/your/repo -type d -print0 | xargs -0 chmod g+s

Then hopefully your git pull should work.