When set, the r, w, and x mode attributes have the following effect on files and
- r Attribute (read permission):
Files: Allows a file to be opened and read.
Directories: Allows a directory's contents to be listed. To retrieve any info about the containing files or directories, the execute attribute must also be set.
- w Attribute (write permission):
Files: Allows a file to be written to or truncated, however this attribute does not allow files to be renamed or deleted. The ability to delete or rename files is determined by directory attributes.
Directories: Allows files within a directory to be created, deleted, and renamed if the execute attribute is also set.
- x Attribute (execute permission):
Files: Allows a file to be treated as a program and executed. Program files written in scripting languages must also be set as readable to be executed.
Directories: Allows a directory to be entered, e.g., cd directory.
Reference: The Linux® Command Line William E. Shotts, Jr.
I would recommend to read this book or pdf version which you can download it from this link: http://sourceforge.net/projects/linuxcommand/files/TLCL/13.07/TLCL-13.07.pdf/download