This command is part of the [TclX] package.

    :   '''umask''' ?''octalMask''?
Gets and sets the [POSIX] file creation permissions mask. Gets the current value if ''octalMask'' is omitted, sets it if ''octalMask'' is given. Will affect the [open] and [file mkdir] commands, plus operations by subprocesses started with [exec] (it is an inheritable property that is cloned when a new process is created).

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