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Print epoch time before and after every issued command in bash

I am trying to modify my ~/.bash_profile so that the Unix epoch time automatically gets printed before and after the execution of every issued command in bash, like so:

[prompt]$ some-maybe-multiline-command
Started execution at: <epoch time>
...
<stuff printed out by some-maybe-multiline-command, if any>
...
Finished execution at: <epoch time>
[prompt]$

How can I achieve this? Ideally, I want to have minimum side effects while doing so (e.g. I do not want this change to affect too many logs if possible); it should ideally only affect what I see on the terminal screen.

Thanks a lot in advance!

I found this answer Unix StackExchange, and tried to adopt it to my situation; but I haven't been successful so far..

Adding trap <command> DEBUG into the ~/.bash_profile is the closest thing to a solution that I found so far. However, I am not sure how to make the <command> be aware of whether it is being executed before or after the execution of the issued command

Solution

  • You can use Bash's PS0 (requires bash 4.4+) and PROMPT_COMMAND.

    According to man bash:

    • PROMPT_COMMAND

      If this variable is set, and is an array, the value of each set element is executed as a command prior to issuing each primary prompt. If this is set but not an array variable, its value is used as a command to execute instead.

    • PS0

      The value of this parameter is expanded and displayed by interactive shells after reading a command and before the command is executed.

    Example:

    PS0='>>> $( date +%s )\n'
PROMPT_COMMAND='echo "<<< $( date +%s )"'

    $ echo hello world; sleep 2
>>> 1686801897
hello world
<<< 1686801899