The user file-creation mode mask is set to mask. This mask affects the initial value of the file permission bits of subsequently created files (see creat(2)).
The mask can be either symbolic form, or octal form. See chmod(1) for a description of the syntax for mask. If mask is in symbolic form, then the umask is set to the logical complement of the result of the symbolic definition. (That is, the symbolic form should specify the permissions to allow through, not the permissions to mask out.) If the mask is in octal form, then each set bit will mask the matching permission (the complement of the symbolic form).
If mask is omitted, the current value of the mask is printed in either symbolic or octal form (see the -S option).
umask is recognized and executed by the shell.
umask can be included in the user's .profile (see profile(4)) and invoked at login to automatically set the user's permissions on files or directories created.
"u=%s,g=%s,o=%s\n" owner_perms group_perms other_perms
Each permissions string has the same meaning as permissions in the arguments to chmod(1).