How can the last command's wall time be put in the Bash prompt?

Question

Is there a way to embed the last command\'s elapsed wall time in a Bash prompt? I\'m hoping for something that would look like this:

[last: 0s][/my/dir]$ sl         


        

Answer 1

Another approach for bash 4.x and above would be to use coproc with PS0 and PS1 like below:

cmd_timer()
{
    echo $(( SECONDS - $(head -n1 <&"${CMD_TIMER[0]}") ))
}

coproc CMD_TIMER ( while read; do echo $SECONDS; done )
echo '' >&"${CMD_TIMER[1]}" # For value to be ready on first PS1 expansion
export PS0="\$(echo '' >&${CMD_TIMER[1]})"
export PS1="[ \$(cmd_timer) ] \$"

This is a .bashrc ready snippet. It is especially useful for everyone that uses undistract-me which overwrites trap DEBUG for its own purposes.

Answer 2

If you hadn't set up any of the other answers before you kicked off your long-running job and you just want to know how long the job took, you can do the simple

$ HISTTIMEFORMAT="%s " history 2

and it will reply with something like

  654  1278611022 gvn up
  655  1278611714 HISTTIMEFORMAT="%s " history 2

and you can then just visually subtract the two timestamps (anybody know how to capture the output of the shell builtin history command?)