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       HISTSIZE

              The number of commands to remember in the command history (see HISTORY below).  If the value is 0, com‐

              mands are not saved in the history list.  Numeric values less than zero result in every  command  being

              saved  on  the history list (there is no limit).  The shell sets the default value to 500 after reading

              any startup files.

       HISTTIMEFORMAT

              If this variable is set and not null, its value is used as a format string for strftime(3) to print the

              time  stamp  associated  with each history entry displayed by the history builtin.  If this variable is

              set, time stamps are written to the history file so they may be preserved across shell sessions.   This

              uses the history comment character to distinguish timestamps from other history lines.