-HistoryNoDuplicates does not have any effect

I have Set-PSReadLineOption -HistoryNoDuplicates in my profile file, and Get-PSReadlineOption shows HistoryNoDuplicates : True. But duplicated entries are being added to the ConsoleHost_history.txt file. I’m using version 1.0.0.13. The following is all the options I have for PSReadLine:

Import-Module PSReadLine

Set-PSReadLineOption -HistoryNoDuplicates 
Set-PSReadLineOption -HistorySearchCursorMovesToEnd
Set-PSReadLineOption -HistorySaveStyle SaveIncrementally
Set-PSReadLineOption -MaximumHistoryCount 4000
# history substring search
Set-PSReadlineKeyHandler -Key UpArrow -Function HistorySearchBackward
Set-PSReadlineKeyHandler -Key DownArrow -Function HistorySearchForward

# Tab completion
Set-PSReadlineKeyHandler -Chord 'Shift+Tab' -Function Complete
Set-PSReadlineKeyHandler -Key Tab -Function MenuComplete

# automatic quotation
Set-PSReadlineKeyHandler -Chord 'Oem7','Shift+Oem7' `
                         -BriefDescription SmartInsertQuote `
                         -LongDescription "Insert paired quotes if not already on a quote" `
                         -ScriptBlock {
    param($key, $arg)

    $line = $null
    $cursor = $null
    [PSConsoleUtilities.PSConsoleReadline]::GetBufferState([ref]$line, [ref]$cursor)

    if ($line[$cursor] -eq $key.KeyChar) {
        # Just move the cursor
        [PSConsoleUtilities.PSConsoleReadline]::SetCursorPosition($cursor + 1)
    }
    else {
        # Insert matching quotes, move cursor to be in between the quotes
        [PSConsoleUtilities.PSConsoleReadline]::Insert("$($key.KeyChar)" * 2)
        [PSConsoleUtilities.PSConsoleReadline]::GetBufferState([ref]$line, [ref]$cursor)
        [PSConsoleUtilities.PSConsoleReadline]::SetCursorPosition($cursor - 1)
    }
}

[vors]

@lzybkr should Set-PSReadLineOption -HistoryNoDuplicates be a default?

[lzybkr]

Shared history relies on the file size to know when to reread history. Trimming history would break that, so another mechanism would be needed to notify other sessions that new history was added.

This would actually be a good thing to add - I just never got around to it.

If I spend any time on history, I’m more likely to replace the simple text file with a sqlite database and would design the schema so duplicates are impossible to add.