Your options here are going to depend on your shell. In
zsh there a convenient hook function called
preexec() that is run right before any interactive shell commands. By creating a function with this name, you can cause things to be executed. You can also follow up with a function called
precmd() which will run just before the next prompt is drawn, which will be right after your command finishes.
By creating this pair of functions, you can have whatever arbitrary commands you want run before and after whatever commands are issued at the prompt. You could use this to log shell usage, create locks, test the environment, or as in your example calculate time or resources spent while a command runs.
In this example, we will create ourselves a benchmark timestamp before running a command using
preexec() then calculate the time spent executing the command using
precmd() and output it before the prompt or log it away. Example:
echo "Last command ran for $CMDRUNTIME nanoseconds."
Note: For this particular example, there is an even easier builtin function. All you have to do is turn on runtime reporting in ZSH and it will do this automatically.
$ export REPORTTIME=0
$ ls -d
ls -BF --color=auto -d 0.00s user 0.00s system 0% cpu 0.002 total
In a more practical implementation of
preexec(), I use it see if the shell is running inside
screen and, if so, to send information about the currently running command upstream to be displayed in the tab name.
Unfortunately in bash this little mechanism doesn't exist. Here is one man's attempt to replicate it. Also see Gilles's answer for similar nifty little hack.