title: Bash (or other shell): wrap all commands with function/script
body: <p>Edit: This question was originally bash specific. I'd still rather have a bash solution, but if there's a good way to do this in another shell then that would be useful to know as well!</p>
  
  <p>Okay, top level description of the problem. I would like to be able to add a hook to bash such that, when a user enters, for example <code>$cat foo | sort -n | less</code>, this is intercepted and translated into <code>wrapper 'cat foo | sort -n | less'</code>. I've seen ways to run commands before and after each command (using DEBUG traps or PROMPT_COMMAND or similar), but nothing about how to intercept each command and allow it to be handled by another process. Is there a way to do this?</p>
  
  <p>For an explanation of why I'd like to do this, in case people have other suggestions of ways to approach it:</p>
  
  <p>Tools like <a href="http://unixhelp.ed.ac.uk/CGI/man-cgi?script">script</a> let you log everything you do in a terminal to a log (as, to an extent, does bash history). However, they don't do it very well - script mixes input with output into one big string and gets confused with applications such as vi which take over the screen, history only gives you the raw commands being typed in, and neither of them work well if you have commands being entered into multiple terminals at the same time. What I would like to do is capture much richer information - as an example, the command, the time it executed, the time it completed, the exit status, the first few lines of stdin and stdout. I'd also prefer to send this to a listening daemon somewhere which could happily multiplex multiple terminals. The easy way to do this is to pass the command to another program which can exec a shell to handle the command as a subprocess whilst getting handles to stdin, stdout, exit status etc. One could write a shell to do this, but you'd lose much of the functionality already in bash, which would be annoying.</p>
  
  <p>The motivation for this comes from trying to make sense of exploratory data analysis like procedures after the fact. With richer information like this, it would be possible to generate decent reporting on what happened, squashing multiple invocations of one command into one where the first few gave non-zero exits, asking where files came from by searching for everything that touched the file, etc etc.</p>