Ubuntu – How to save live log bash input to a file

bashcommand linelogging

When I am teaching a class, some students have problems following my CLI commands and would like to scroll back to be able to repeat the steps in their own speed. So I'd like to log all my inputs in realtime to an html-file or something similar, which I could server through a webserver. That way, the students could simply go to http://example.com/log#end and would always see the last entries.

I do know the multiuser mode of screen and have already used it to share sessions. However, I need to disable the write access of students and unfortunately, they are unable to scroll up, if I do so.

I also had a look at script, but it generates a terrible output, which – even when filtered through col -bp < logfile >> output.html is unreadable. Also, it does log the output as well, which complicates things and only dumps the logfile in unforeseeable intervals.

.bash_history could be used, but is only dumped to file when the session ends.

Any ideas?

Best Answer

Use the built-in command history:

history -w hist.txt

will save the current history into file hist.txt.

If you have write permsiions to the appropriate directory you could do something like:

history -w /var/www/html/latest_history.txt

Then your students could access it in a browser: http://teachers.ip.address/latest_history.txt

Related Solutions

Ubuntu – How to log all Bash commands by all users on a server

For BASH shells, edit the system-wide BASH runtime config file:

sudo -e /etc/bash.bashrc

Append to the end of that file:

export PROMPT_COMMAND='RETRN_VAL=$?;logger -p local6.debug "$(whoami) [$$]: $(history 1 | sed "s/^[ ]*[0-9]\+[ ]*//" ) [$RETRN_VAL]"'

Set up logging for "local6" with a new file:

sudo -e /etc/rsyslog.d/bash.conf

And the contents...

local6.*    /var/log/commands.log

Restart rsyslog:

sudo service rsyslog restart

Log out. Log in. Voila!

But I forgot about log rotation:

sudo -e /etc/logrotate.d/rsyslog

There is a list of log files to rotate the same way...

/var/log/mail.warn
/var/log/mail.err
[...]
/var/log/message

So add the new bash-commands log file in that list:

/var/log/commands.log

Save.

Ubuntu – How to save terminal history to a file from a bash file

Short Answer

Run the script with source or .:

source ./script_name.sh

. ./script_name.sh

The latter is slightly more compatible across different shells.

Long Answer

This question highlights an important point, which is that shell scripts are run in their own context. To see what this means, consider the following shell script:

#!/bin/bash

cd /
ls

If you run this, you will get an output something like this:

bin  boot  dev  etc  home  lib  lib64  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

But you will notice that after you run the script, you are still in whatever directory you were in before you ran it: the cd / inside the script hasn't actually affected your session - it only affected the context which the script was running in, which is created for the script to run in, and destroyed once it returns.

The source command will 'read and execute commands from the filename argument in the current shell context', so any commands like cd inside it will affect your current session. If you were to run the script above by passing it to source you would find that you end up inside the root directory after it ran.

In this case, the problem is that the history command gives you the history for the current shell context; the shell context that your script runs in without using source has no history, so it doesn't write anything to the output file. If you use source it will execute in the correct context, and will work as expected.

N.B.: source is a shell built-in, not a program per se - in Bash, source is synonymous with ., but in some shells only . will work - I've used source in this answer because it's easier to read than ., but for maximum compatibility, . should be used.