Fun with chmod

To carefully add permissions to files in a directory tree, keep capital letters in mind.

The following is dangerous:

chmod -R a+x directoryname

That would give execute permissions to all files underneath directoryname.

To give execute permissions to only files that currently have execute permissions use:

chmod -R a+X directoryname

That would give execute permissions to only those files that already have some other execute permission -- great for allowing others to look in directories.

Fun.