Write bash_history to a file with a timestamp

Question

The requirement is to capture command line history in a file with specific date and time of commands, when they were executed.

The below script captures history with date and time but it also assigns the current date and time for older commands. Also I want to extend the script to take incremental backup of the history output file.

#!/bin/bash
. ~/.bash_profile
HISTFILE=~/.bash_history
set -o history
history >/home/user/hist_`date "+%d%b%y%T"`

Answer 1

Not quite what you wanted, but you can get bash to add timestamps to each line in the history automatically. Simply set, for your example:

HISTTIMEFORMAT="%d%b%y%T "

The history command with no arguments will then show your history entries like this:

23Jul1515:48:14 ls -ld .

The history -w command however always writes the history file in the internal format of:

#1437659315
ls -ld .

i.e. on 2 lines, the first line holds the time in seconds "since the epoch" (i.e. 1 jan 1970) with a # in front so that it will not be confused with a command.

Answer 2

In bash, there is an option that instructs bash to record a timestamp with each command. You do this by assigning a useful value to the environment variable HISTTIMEFORMAT. From the bash manpage:

If this variable is set and not null, its value is used as a format string for strftime(3) to print the time stamp associated with each history entry displayed by the history builtin. If this variable is set, time stamps are written to the history file so they may be preserved across shell sessions. This uses the history comment character to distinguish timestamps from other history lines.

Note, after having activated HISTTIMEFORMAT then ~/.bash_history will have always two lines per each recorded command:

• First a line starting with a hash "#" symbol, immediately followed by a Unix timestamp (seconds since start of the Unix epoch).
• Second a line which is the command as you typed it.

  #1671097644
  cd ~/bin
  #1671097645
  ls -l
  

In my environment, I use

HISTTIMEFORMAT="%s (%H:%M:%S):"

When you invoke history that tool formats the timestamp on the fly with your defined format. I use above formatting so that commands may be sorted easily (%s is timestamp in seconds) and human-readable. In my shell, when I type history, I see something like the following:

3  1437664568 (17:16:08):man bash
4  1437664699 (17:18:19):history

Note: All commands prior your activation of timestamp recording, are only the command without the prefixed timestamp line. Hence they show the date/timestamp when you logged into your current session. If that annoys you, then simply do a find/replace of your legacy lines to prefix them with an artificial timestamp. And add a note on the boundary line for documentation purposes. Like this:

#1671058800
ls -l
#1671058800
exit
#1671094600
echo Activated timestamp recording in the history file now.
#1671094610
echo All commands prior got the artificial timestamp 2022-12-15 00:00:00 (1671058800).
#1671094622
cd /
#1671094627
exit

EDIT: OPs question not fully answered.

Also I want to extend the script to take incremental backup of the history output file

I'm not sure what you mean by "incremental backup" of the history file. Perhaps you simply want the history backed up periodically. There are a couple of approaches you can take:

• Set PROMPT_COMMAND variable with history -a to continually update the history command after every invocation (as opposed to waiting for logout).
• Trap the DEBUG signal with a function you define. Every time a command is entered, the function will be called. From within the function you can do everything. (Slightly more reliable than PROMPT_COMMAND).
• cronjob to periodically copy/archive the history file.