[saurik]

Omg, I just read the documentation for erasedups and I'm actually shocked anyone would want that feature turned on, to the point where it never even would have occurred to me to implement it in the first place and if the feature worked like that without some way to turn it off I'd have been super angry :(. Maybe we are parsing that sentence wrong and by "shouldn't be necessary to set" the idea is "it is useful in situations where you have limited disk space / memory but in the 21st century no one would need to set this so it might as well no longer be supported"?

[adrian_b]

That option has nothing to do with limited disk space.

Eliminating the duplicates makes it much easier to search the history for a command that was used long ago instead of having to skip over hundreds of duplicates of some non-interesting command, such as "ls".

It also makes it much more likely that complex commands used a long time are still preserved. No matter how large you make your history file, it is much more likely that it will become filled with simple commands that you do not need to recall from history, instead of keeping the complex commands that you hate to retype.

Moreover, while having a command history is useful to avoid retyping some commands, some may be less willing to preserve a history from which it is easy to discover which have been their exact actions while using the computer, though for this it is preferable to also disable the saving of the history file.

[TRiG_Ireland]

    $ cat ~/.inputrc 
    "\e[A": history-search-backward
    "\e[B": history-search-forward

This means that I can type the first couple of letters of a command, and then use the up and down arrow keys to cycle through history to search the rest of it. It makes life simpler for me, and confuses me only on the occasions when I've used `git stash`, so `git status` doesn't appear when I expect it to.

[post-it]

fish shell does this by default, and also autocompletes commands from your history. I highly recommend it.

[JoshTriplett]

Ctrl-O is incredibly useful. Go back to an earlier command, press Ctrl-O repeatedly, and you re-run a series of commands. That doesn't work if some of them were deleted as duplicates.

[pdw]

Now I'm confused. Why would you want duplicate entries in your command history? I get that on an overloaded system in the 80s it might have taken a perceptable amount of time to filter out duplicates. But on a modern system you surely want it always enabled?

[jxf]

I think the people who leave it on see it as "rewriting history" -- e.g., if you typed [cmd1], [cmd1], [cmd2], and you erase duplicates, your history no longer reflects what you actually typed. The people who leave it off see the history as more like "a list of interesting things I did at some point", so erasing duplicates means it's easier to find the most interesting things.

[hansvm]

Any search of the form "what other interesting commands did I need the last time I did <foobar>?" benefits from being able to see the historical context. Or if I know the particular incantation is one I wrote several times and is very similar to some others then it's easy to search the history for the blocks of popular commands. Or whatever. It's your terminal, but given how fuzzy the interconnects in a mind can be it's hard to know what info might be useful down the road.

To your point about computing power, I think it's only now that it's reasonable to not filter the duplicates. If I want to emulate the dedup behavior it's trivial nowadays to blindly read 1M lines of history and dedup on the fly each time. Using downstream tools doing duplicate filtering/transforming work is similarly very very fast. Disk is cheap enough that I really do want to keep every command I ever write in my history. More expensive compute and disk would make me more likely to turn that feature on, not less.

[msm_]

I don't use bash so it's not applicable to me anyway, but why would I want it on? It's saving a few bytes of disk space, at the cost of ruining my history (the thing that the whole feature is about). At least fish's search feature is so awesome that I never had a problem with duplicate commands causing problems.

And I want my history untouched, because sometimes I forget how I solved something, go back a few months in my shell history and see the sequence of commands that I've used. I think that's a nice thing to have. And if I ever need history without duplicates, it should be easy to deduplicate it with a simple script.

[nullc]

I use ignoreboth -- it's not about saving disk and memory, it's about making the history more useful for searching. The ignorespace also helps avoid getting credentials saved to disk you don't want saved and is even more useful these days than it was in the past because we're no longer on multiuser systems where you really want to keep credentials out of commandlines entirely.

[kayodelycaon]

I have the HIST_IGNORE_ALL_DUPS options set on zsh. I only need a history of what commands I have run, the order isn't important to me. Having the history be a unique set of commands makes it easier to dig through.