Why do the line numbers shown by the history command differ from the line numbers of the history file displayed by less and wc -l?

Question

The line numbers from less -N .bash_history and wc -l .bash_history have 44 more lines than the line numbers shown by the bash built-in command history. Comparing the last 20 entries in the history list displayed by history against the last 20 entries in the history file displayed by less shows that those commands are the same, which rules out duplicate commands as the reason, so what is causing the different line numbers between the history command and wc or less?

I initially assumed that the history command simply counted the commands in the history file but the different results with less -N or wc -l indicate this is not the case

Answer 1

This is due to the bash_history may be recording the Epoch timestamp of every command.

HISTTIMEFORMAT environment variable is set in the bashrc file as HISTTIMEFORMAT="[%F %T] "), bash stores timestamps for each history item and when a user inspects history with the BASH built-in history, the timestamps are shown in an easily-readable format (ex: 2019-07-24 15:40:19); however, when these history sessions are saved out to a file (e.g., ~/.bash_history), the timestamps are shown in Unix time (seconds since the Epoch).

You may use history with option -r or -w to input the .bash_history file.

https://ss64.com/bash/history.html

I hope this answers your question.