Track elapsed time in milliseconds on ZSH

elapsed_ms.zsh

# This code snippet is dedicated to the Public Domain, or licensed under CC0 if you prefer.

printf -v _start '%.0f' $(( EPOCHREALTIME * 1000 ))
::
::: COMMANDS TO MEASURE HERE :::
::
printf -v _end '%.0f' $(( EPOCHREALTIME * 1000 ))

_elapsed=$(( _end - _start ))

# Bonus: Print elapsed time in unit of seconds:

# The space " " after the colon ":" in the second substitution is REQUIRED!
# Without the space, it will be interpreted as ":-" (substitute if none) rather than ":" (substring)
echo "Those commands took ${_elapsed::-3}.${_elapsed: -3} seconds to complete."

# If you dislike trailing zeroes after the decimal separator, process _elapsed first.
# I shall leave that to you because I personally don't see the need.

Please note that THIS DOES NOT WORK IN bash !!

The simple reason being that bash does NOT support floating-point arithmetics within (( )), so Lines 3 & 7 there will result in a Syntax Error.