time part of a script (running time) - linux

Question

With the time script.sh you will get the time it took to run a script, BUT if you want to time a part of the script?
let's say I want to test how long a loop takes, I could use the $SECONDS function, but is there any timer that counts milliseconds?
for example in the middle of a long code:
timerstart
until [[ $loop -eq 10000 ]]; do
((++loop))
echo "annoying"
done
timerstop
and then in the end of the script, I just add echo $timerresult , and it will display how many milliseconds it took to run only the selected code, and not the rest of the script
I'm looking for this solution so I can test parts of scripts for "slowness"..
is this possible to solve?

Answer 1

For Bash 5.0 and later, you can use $EPOCHREALTIME:
[...] it expands to the number of seconds since the Unix Epoch as a floating point value with micro-second granularity [...]
start=$EPOCHREALTIME
for ((i = 0; i < 10000; ++i)); do
echo "annoying"
done
stop=$EPOCHREALTIME
elapsed=$(bc -l <<< "$stop - $start")

Answer 2

You can use
date '+%s.%N'
to get the current time with nanosecond precision.
#!/bin/bash
start=$(date '+%s.%N')
until [[ $loop -eq 10000 ]]; do
((++loop))
echo "annoying"
done
stop=$(date '+%s.%N')
bc <<< $stop-$start

Answer 3

You can use time in the script for individual parts too, e.g. to time the loop:
time until [[ $loop -eq 10000 ]]; do
((++loop))
echo "annoying"
done
or with a brace group to time a group of commands:
time {
until [[ $loop -eq 10000 ]]; do
((++loop))
done
echo "Other commands here that are also timed"
}

Answer 4

Put the loop in a function.
#!/bin/bash
myloop() {
loop=1
until [[ $loop -eq 10000 ]]; do
((++loop))
echo "annoying"
done
}
time myloop