Add an option to remove only consecutive history duplicates

Environment data

PS version: 5.1.17134.228
PSReadline version: 1.2
os: 10.0.17134.1 (WinBuild.160101.0800)
PS file version: 10.0.17134.1 (WinBuild.160101.0800)

Description

PSReadline has the option Set-PSReadlineOption -HistoryNoDuplicates (The plain Windows console has the equivalent “Discard Old Duplicates”), this option removes all duplicate history entries, even non-consecutive ones. For example: Typing the commands echo 1, echo 2, echo 2, echo 1, the history will be echo 1, echo 2.

Bash has the option HISTCONTROL=ignoredups, and Zsh has HIST_IGNORE_DUPS. These options only remove consecutive duplicates. For example: Typing the commands echo 1, echo 2, echo 2, echo 1, the history will be echo 1, echo 2, echo 1.

I think the Bash/Zsh behavior is way more intuitive and useful than removing all duplicates and it would be a great feature for PSReadline to have.

EDIT: There is also the related HISTCONTROL=ignorespace, HIST_IGNORE_SPACE which is also nice to have and probably quite easy to implement.

[lzybkr]

HIST_IGNORE_SPACE is easy - you can add something like this to your profile:

Set-PSReadLineOption -AddToHistoryHandler {
    param([string]$line)
    return $line.Length -gt 3 -and $line[0] -ne ' ' -and $line[0] -ne ';'
}

This example will ignore short commands (3 or less) and commands that start with a space or semi-colon.

I thought I had this example in the sample profile but apparently not.

[daxian-dbw]

For example: Typing the commands echo 1, echo 2, echo 2, echo 1, the history will be echo 1, echo 2.

The reported issue has been addressed in PSReadLine (I guess it was done quite a while back). Now HistoryNoDuplicates only removes consecutive duplicates.