Bash – How to reverse the bash history list

I posted this question on the help-bash mailing list and got a response from Chet Ramey, the maintainer of Bash.

He suggested adding either of the following before the history -s command:

set -H    # aka set -o histexpand

or

histchars='!^#'

I tried each of them and they both work. The reason is that the history comment character which defaults to # hasn't been set at the point that the profile code is running and so is null (\0).

Here's my working file:

HISTTIMEFORMAT='%c : '
histchars='!^#'
set -o history
history -s "# some text as a marker"

This was a hack I used once on a shared account to track who did what:

PROMPT_COMMAND="history -a; sed -i '\$s/\$/ \#$NAME/' $HISTFILE; history -r; $PROMPT_COMMAND"

It writes the history before the PROMPT is displayed: in effect, after each command. You could modify this to use save the exit code in the history:

PROMPT_COMMAND="CODE=$?; history -a; sed -i '\$s/\$/ \#\$CODE/' $HISTFILE; history -r; $PROMPT_COMMAND"

This would leave entries in your history like:

$ history 2
 1271  vim .bashrc #0
 1272  history 2

(The last entry will be updated, after the history command exits, so the exit code isn't visible in this output.)

This has the annoying effect that history in your prompt will have the comment:

$ # press up
$ history 2 #0

The comment doesn't affect execution or output usually, but makes editing a pain.

Now you can grep your history to see which codes exited successfully:

history | grep '#0$'
# or grep '#[^0]*$' for unsuccessful commands.