Warning running with shell_exec

[dspstudio]

I'm getting a warning when i call shell_exec from PHP , if i run it from terminal everything works.
I think it might be with the apache rights If so what permissions should i give.
command used in PHP: shell_exec("/usr/local/bin/python2.7 /usr/local/bin/youtube-dl $input -g -i 2>&1")

WARNING: Writing cache to u'//.cache/youtube-dl/youtube-sigfuncs/js_vfltYLx8B_43.40.json' failed: Traceback (most recent call last):
File "/usr/local/bin/youtube-dl/youtube_dl/extractor/youtube.py", line 481, in _extract_signature_function
os.makedirs(os.path.dirname(cache_fn))
File "/usr/local/lib/python2.7/os.py", line 150, in makedirs
makedirs(head, mode)
File "/usr/local/lib/python2.7/os.py", line 150, in makedirs
makedirs(head, mode)
File "/usr/local/lib/python2.7/os.py", line 157, in makedirs
mkdir(name, mode)
OSError: [Errno 13] Permission denied: '//.cache'

[phihag]

In order to not have to download player files (which never change), youtube-dl caches some files in a directory relative to $HOME. We may also extend the cache in the future.

I recommend one of the following options:

• Pass in --no-cache-dir. This will disable caching though and will have a negative impact on performance.
• Pass in --cache-dir /tmp/youtube-dl or any other cache directory instead of /tmp/youtube-dl. The directory should be writable, readable, and indexable for the apache user, but that should be the default for/tmpand/var/tmp` already.