i have changed permissions in /var/www into 775 with:
chmod -R 775 /var/www

however when i create a new file from nautilus it has permissions 500
this means that it's not available to the group and also that
i have to chmod all my php scripts when i create them. new files and dirs created from command line have 755

How can i do it so that every new file or dir created either from nautilus (or other software) or from the command line to have the /var/www's permissions (aka 775)

thanks

Check that out :
http://blogs.gnome.org/view/cneumair/2005/12/26/0
http://blogs.gnome.org/view/cneumair/2005/12/28/0

Nice link but not what i was looking for.
My problem is not how to change permissions recursively but also how to make all newly created dirs and files inherit permissions from the parent directory (like it happens in windows).

For example my /var/www is 775 and when i create a new file as a user of the group that owns /var/www it has permissions 644. I would expect (or wish at least) everything created inside /var/www to have 775 permissions...

This is impossible, file permissions cannot be inherited in this way. You can set the default file permissions with an appropriate umask (012 or 002) but you cannot set execute permission with umask, you have to use chmod for this. If you're too lazy to type chmod after creating a script (as you should be, laziness in a programmer being a virtue of course), then you can write a wrapper script around your text editor to do it automatically based on file extension (.php, .sh etc).

Personally I write all my scripts in ~/src/sh, ~/src/python etc and install them with an 'installscript' script, which does a chmod +x and copies it to ~/bin or wherever. This lets me edit/test scripts without munging a working version, which may be still in use.

omg ! It's a huge limitation for any OS and a pitty that linux can't inherit permissions.
However the 'installscript' script is a nice idea (or perhaps a 'newscript' script) and will make my life easier. Thanks

To set the default file permision to 775 use

umask 002

Will that change the default file permissions globaly ? For all sessions ?

I am fairly sure you can achieve it using ACLs:

http://www.vanemery.com/Linux/ACL/linux-acl.html

Oh, yeah, I expect so (never used them myself). I just meant you can't do it with the default unix permissions mechanism.

It would be handy in some situations, but I wouldn't call it an essential feature.

That won't automatically set execute permissions though, which is what thejasondean wanted.

Unless otherwise specified, when a file is created the permissions are determined from the umask. The resulting permissions are 666 logically anded with the umask. Most distros use a default umask of 022, which results in 644 file permissions. This applies to the current shell, and will be inherited by processes spawned by the shell (though of course, processes can change their umask at will). As I mentioned before though, you cannot set execute permissions automatically via the umask. There is also no way to force particular file permissions globally with the standard unix permissions mechanism, though you should be able to achieve it with ACLs as magnus.therning pointed out.