what does this command mean "history -d $((HISTCMD-1))"

from the command history, I see a command like this:

history -d $((HISTCMD-1))

I don't understand what this command does, could you please help.

thanks.
Jason YuAsked:
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woolmilkporcCommented:
history is a command to manipulate the command line history.

Its "-d" flag is used to delete a command at a specific position (offset).

HISTCMD is a variable containing the future sequence number of the next command.

$(( )) is a shell construct to perform arithmetic operations.

So your command will delete the "current" entry from the shell's history, i. e. the "history -d ..." command itself - for whatever it's worth.
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Jason YuAuthor Commented:
thank you very much, I got it. it's the user wanting to hide his commands.
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