mjhjmtu

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.

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.

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 ))"