@Mike:
Thanks for the hint, I didn't know about that command. (But there are so many little-used commands.....)

history_control does have a few limitations:

1. ignoredups only works on the previous command.
So running e.g., a short or long) for loop (with a series of different commands) in the debugger will still fill up the history.
This is my main gripe of comment #1.

2. erasedups didn't seem to work at all on my 3.9.0+ build.
What I did is:

history_control erasedups

and then entered a few commands matching commands typed earlier. Nothing changed in the behavior of the history pane.

However, after restarting Octave the duplicates were gone in the history pane and when using the up-arrow key.
So apparently the history pane isn't updated upon calls to 'history_control erasedups'.

@Michael:
As the CLI is part of the GUI, both have the same capabilities as regards history_control. Or do you refer to the OP's request (which I support as well)?

@Philip: you can do that already using the history_control function. Use `history_control ignore_dups` to have it automatically filter out duplicate lines. Works in both CLI and GUI.

Deleting history entries should just require calling command_history::remove. If this were supported in the GUI, it should probably be supported in CLI with a callable function also. Or it could be an option to the history command, `history -d N` for example, as in bash. Reassigning to the interpreter for now.

Add a "Delete" menu item to the right click menu of the command history list (and make sure the Delete also works for a multi-selection of list entries as it does for the other actions available like Copy, ...).