Print the current value of the file creation mode mask, or
set it to
value, a three-digit octal code specifying
the read-write-execute permissions to be turned off. This
is the opposite of chmod.
Usually used in .login or .profile.
umask is available as a built-in command in the Bourne and C shells
(see Sections 4 and 5).
Turn off write permission for others:
umask 002 Produces file permission -rw-rw-r-
Turn off all permissions for group and others:
umask 077 Produces file permission -rw----
Note that you can omit leading zeroes.