Professor Donald E. Knuth, Author of the Holy “The Art of Computer
Programming” books and Creator of the Powerful Document Preparation
Tool, LaTeX. URL: http://www-cs-faculty.stanford.edu/~knuth/

One Day One Command
===================

umask — Default file-creation permission mask.

Summary:

umask is used to set the default permission for files, which is
created by the user. To get the actual default permissions, the
mask should be XOR-ed with 0666 for files and 0777 for folders.

For example, if umask is 0002, then (0002 ^ 0666) = 0664 is the
default permission for files.     

Examples:

$ umask — Show the mask value in Number form.

$ umask -S — Show the mask value in Symbolic form.

$ umask 0022 — Set the default mask as 0022.

$ umask u=rwx,g=rx,o=rx — Same as above, in Symbolic mode.

Read: help umask