I made a few tweaks to the language and checked the change in under your name on the stable branche of Octave.  See https://hg.savannah.gnu.org/hgweb/octave/rev/8c9924a425db.

This will be a part of the next bug fix release of Octave.

Marking as fixed and closing report.

Thanks for the additional hints. And sorry, I don't intend to open a seperate bug report for all of my "support" questions, in general.

Yes, I think adding some explanations to the help string of the history_file command would be useful.

Here is my suggestion for this:

VAL = history_file ()

OLD_VAL = history_file (NEW_VAL)

Query or set the internal variable that specifies the name of the
file used to store command history.

All future Octave commands issued during the current Octave session
will then be written into this new file (if the current setting of
"history_save" allows for this).

The default value for the history file is '~/.octave_hist', but this
may be overridden by the environment variable 'OCTAVE_HISTFILE'.

Notes:

* If you want to permanently change the location of Octave's history
file you need to reissue the "history_file" command in every new Octave session.
This can be achived by using Octave's ".octaverc" startup file.

* If you also want to read the saved history commands of past Octave sessions
from this different history file, then you need to use the additional command
"history -r" after setting the new value of the history file. A useful code
in Octave's startup file to do this could look like this:

   history_file ("~/new/.octave_hist");
   if (exist (history_file ())
     history -r
   endif


See also: history, history_size, history_save,
history_control, history_timestamp_format_string.

I tried to use the Octave command "history_file()" for what I think it's ment for, but it doesn't work properly.

Here is a way to reproduce it:

• change your .octaverc or startup.m file such that it contains the following line of code: "history_file('~/test/.octave_hist');"
• delete the already existing history file ".octave_hist" in your home folder (and maybe all other existing .octave_hist file in your system).
• start Octave
• type some commands into Octave, e.g. "123+456" and execute them
• close Octave again
• look into the folder "test", it will now have the history file ".octave_hist" that properly contains your freshly typed commands. So far, so good.
• now restart Octave
• look at the history (it will be empty), or type the "arrow up" key in the command window (nothing will show up)

I have observed this behavior with Octave 5.1 release, under Win10 as well as under (Ubuntu) linux. Since I assume that this command "history_file()" used to work properly at some time ago (the descsribed use case is the only one this Octave command seems to have) I classified this bug report as "regression".

(Maybe there is only the "append" option missing in this case of a non-standard file location of the Octave history file?)