I have a simple code to ensure a script takes at least x seconds (500 here) on Ubuntu
t1=$(date +%s)
# script is here
t2=$(date +%s)
let "t = 500 - $t2 + $t1"
(( t = t>0 ? t : 1 ))
sleep $t
The code works perfectly, but I believe my coding is not efficient, and these three lines
t2=$(date +%s)
let "t = 500 - $t2 + $t1"
(( t = t>0 ? t : 1 ))
should be expressed in one single line. My question is how to improve the code.
What your script is, is non-portable (since you're using let and (( .. ))), confusing (since you're using both let and (( .. ))), lacking in documentation (there are no comments, and the variable names are non-descriptive), and marginally unsafe (since you haven't quoted the expansion of $t).
If you want a rewrite, here's mine:
#!/bin/sh
min_duration=500
t_start=$(date +%s)
# script is here
t_end=$(date +%s)
elapsed=$(( t_end - t_start ))
# sleep long enough to make sure 'min_duration' seconds has elapsed,
# but at least 1 second
sleep "$(( elapsed < min_duration ? min_duration - elapsed : 1 ))"
: "$(( elapsed = t_end - t_start ))" and simply (( elapsed = t_end - t_start ))?
set -e. Personally, I think I would have used elapsed=$(( ... )). Also notice that he's writing for /bin/sh, not bash.
dash and busybox don't support (( .. )). With Bash, I'd use (( .. )) since it looks less ugly to me. The exit status shouldn't matter (well, unless someone uses set -e, but let's not go there...)
elapsed=$((..))... Thanks.
Here is how I would do it using bash special parameter SECONDS:
#!/bin/bash
SECONDS=0
# script is here
sleep "$(( 500 > SECONDS ? 500 - SECONDS : 1 ))"
Normally SECONDS returns time (in seconds) since the script has started, but one can assign any value to (re)set the timer.
SECONDS doesn't hurt, and at least makes the initial value explicit, but since it tells the time since the script started you don't have to zero it. Unless the script does something else first, of course.
A simple alternative is to just run sleep in in the background and then wait for it after running the other code.
#!/bin/bash
sleep 500 &
# script is here
wait
date?)sleep, how are you going to unravel that when someone calls you at 4 in the morning the day after a most raucous party to debug it when it goes sideways?tandt2entirely, but make sure your phone is switched off at 4am.sleep $( printf "%d\n" $(( 500 - ($(date +%s) - t1) )) | sed 's/^-.*/1/' )