umask
Gets or sets the process file-creation permission mask.
With an argument, sets the umask to the given value and returns the previous mask. Without an argument (or with undef), queries the current mask by temporarily setting it to 0 and restoring it, then returns the value.
The umask affects the default permissions of newly created files
and directories. The actual permissions are requested & ~umask.
Returns the previous umask as an integer (typically displayed in octal).
Synopsis
my $old_mask = umask(0022); # Set new mask, return old
my $current = umask(); # Query current mask