HISTCONTROL=ignoreboth doesn't work

Question

The default .bashrc in the standard distribution of Ubuntu 16.04 that comes with AWS has these lines:

# don't put duplicate lines or lines starting with space in the history.
# See bash(1) for more options
HISTCONTROL=ignoreboth

However, it doesn't seem to work. I have been running pm2 restart myApp and pm2 list repeatedly using the Up Arrow key, and the command buffer now contains nearly a hundred lines of these.

What could be wrong?

Solution

It's working as intended. ignoredups, implied by ignoreboth, doesn't add a command to history if it's the same as the immediate previous command. It doesn't look further back in history. From the manual:

A value of ‘ignoredups’ causes lines which match the previous history entry to not be saved.

So, this will add foo twice to the history:

$ foo
$ bar
$ foo

But so will this:

$ foo
$ bar
$ foo
$ foo

The last foo won't be added to history, since the previous command was foo. Use erasedups in conjunction:

A value of ‘erasedups’ causes all previous lines matching the current line to be removed from the history list before that line is saved.

So:

HISTCONTROL=ignoreboth:erasedups

Comments

[phuclv]

Why does bash still keep duplicate lines with erasedups?

[Jerry Green]

That is the problem: it doesn't work. I run foo 3 times in a row, exit bash, lookup history, - and it contains 3 foo! I am using zsh 5.8 (x86_64-apple-darwin20.0) / GNU bash, version 3.2.57(1)-release (x86_64-apple-darwin20) (default on macOS Big Sur)