Linux – bash command history update before execution of command

bashhistorylinuxshell

Bash's command history is great, especially it is useful when adding the history -a command to the COMMAND_PROMPT.

However, I'm wondering if there is a way to log the commands to a file as soon as the Return key is pressed, e.g. before starting the command and not on completion of the command (using the COMMAND_PROMPT option would save the command once the prompt is there again).

I read about auditing programs like snoopy and session recorder like script but I thought they're already too complex for the simple question I have. I guess that deactivating that script logs all the output of the command would lead already in the right direction but isn't there a quicker way to solve that probelm?

Thanks,
Jon

Best Answer

The DEBUG trap is executed before each command. You could set up a trap and in that do your logging.

Related Solutions

Bash – How to Execute a Command Before Every Bash Command

Sorry for the wrong answer before, I missunderstood your question.

To have the time added before every command that you execute on the shell you can do something like this

bind 'RETURN: "\e[1~time \e[4~\n"'

This will rebind the return key. Now every time you press return instead of writing a newline \n it will go to the beginning of the line, enter the text 'time' and a space, go to the end of the line and enter the newline \n thereby producing the desired effect.

If you don't want to sacrifice your Enter Key you could make a 'second' benchmark-enter Key like F12 by binding the command like this

bind '"\e[24~": "\e[1~time \e[4~\n"'

Now instead of replacing the return key you bound F12.

The background of all this is that bash uses GNU readline to read commands. So readline would be a good starting point for further command manipulation, etc.

How to get infinite command history in bash

it is indeed not (well) documented and I guess 99% of the bash user on this planed do set HISTSIZE to a veeery large number.

In the GNU bash history is handled through the mighty readline library. The library has the option to limit the history size ("stifle" in readline jargon) or not and bash simply sets the readline history to stifled/unstifled. If you look into e.g. GNU bash version 4.2, file variables.c, line 4443, function void sv_histsize (char*) you'll find this comment (and the whole stifling/unstifling in the function that follows):

/* What to do after the HISTSIZE or HISTFILESIZE variables change.
If there is a value for this HISTSIZE (and it is numeric), then stifle the history. Otherwise, if there is NO value for this variable,
unstifle the history. If name is HISTFILESIZE, and its value is
numeric, truncate the history file to hold no more than that many
lines. */

So this should do the trick:

export HISTSIZE=""

And also this (if you feel defiant):

export HISTSIZE="GOTCHA"

Hope this helps.

Best Answer

Related Solutions

Bash – How to Execute a Command Before Every Bash Command

How to get infinite command history in bash

Related Question