The default values for the number of column positions, COLUMNS, and screen height, LINES, are unspecified because historical implementations use different methods to determine values corresponding to the size of the screen in which the utility is run. This size is typically known to the implementation through the value of TERM, or by more elaborate methods such as extensions to the stty utility or knowledge of how the user is dynamically resizing windows on a bit-mapped display terminal.

The default values for the number of column positions when COLUMNS is unset or null, and screen height when LINES is unset or null, are unspecified if the terminal window size cannot be obtained (from tcgetwinsize()) because historical implementations use different methods to determine the values.