chmod

Reference 	Class 	Description
u 	user 	the owner of the file
g 	group 	users who are members of the file's group
o 	others 	users who are neither the owner of the file nor members of the file's group
a 	all 	all three of the above, same as ugo


Operator 	Description
+ 	adds the specified modes to the specified classes
- 	removes the specified modes from the specified classes
= 	the modes specified are to be made the exact modes for the specified classes

Mode 	Name 	Description
r 	read 	read a file or list a directory's contents
w 	write 	write to a file or directory
x 	execute 	execute a file or recurse a directory tree
X 	special execute 	which is not a permission in itself but rather can be used instead of x. It applies execute permissions to directories regardless of their current permissions and applies execute permissions to a file which already has at least one execute permission bit already set (either user, group or other). It is only really useful when used with '+' and usually in combination with the -R option for giving group or other access to a big directory tree without setting execute permission on normal files (such as text files), which would normally happen if you just used "chmod -R a+rx .", whereas with 'X' you can do "chmod -R a+rX ." instead
s 	setuid/gid 	details in Special modes section
t 	sticky 	details in Special modes section


command 	explanation

chmod a+r publicComments.txt 			read is added for all classes (i.e. User, Group and Others).
chmod +r publicComments.txt 			omitting the class defaults to all classes, but the resultant permissions are dependent on umask
chmod a-x publicComments.txt 			execute permission is removed for all classes.
chmod a+rx viewer.sh		 		add read and execute for all classes.
chmod u=rw,g=r,o= internalPlan.txt 		user(i.e. owner) can read and write, group can read, Others cannot access.
chmod -R u+w,go-w docs 				add write permissions to the directory docs and all its contents (i.e. Recursively) for user and deny write access for everybody else.
chmod ug=rw groupAgreements.txt 		User and Group members can read and write (update the file).
chmod 664 global.txt 				sets read and write and no execution access for the user and group, and read, no write, no execute for all others.
chmod 0744 myCV.txt 				equivalent to u=rwx (400+200+100),go=r (40+ 4). The 0 specifies no special modes.
chmod 1755 findReslts.sh 			the 1000 specifies set sticky bit and the rest is equivalent to u=rwx (400+200+100),go=rx (40+10 + 4+1) This suggests that the script be retained in memory.
chmod 4755 SetCtrls.sh 				the 4 specifies set user ID and the rest is equivalent to u=rwx (400+200+100),go=rx (40+10 + 4+1).
chmod 2755 SetCtrls.sh 				the 2 specifies set group ID and the rest is equivalent to u=rwx (400+200+100),go=rx (40+10 + 4+1).
chmod -R u+rwX,g-rwx,o-rx PersonalStuff 	Recursively set a directory tree to rwx for owner directories, rw for owner files, --- (i.e. no access) for group and others.
chmod -R a-x+X publicDocs 			remove the execute permission on all files in a directory tree (i.e. Recursively), while allowing for directory browsing.