If n is omitted, the default is 10. The tab-stop values will be positive decimal integers in strictly ascending order. If LANG is unset or null, the corresponding value from the implementation-dependent default locale will be used. If any of the internationalisation variables contains an invalid setting, the utility will behave as if none of the variables had been defined. If set to a non-empty string value, override the values of all the other internationalisation variables.
TERM Determine the terminal type.
If this variable is unset or null, and if the -T option is not specified, an unspecified default terminal type will be used. If standard output is a terminal, the appropriate sequence to clear and set the tab stops may be written to standard output in an unspecified format. If standard output is not a terminal, undefined results occur. An error occurred. This utility makes use of the terminal's hardware tabs and the stty tabs option.