What’s the Best Way to Measure Command Execution Time?

When I need time in milliseconds, I usually define a shell function like this:
```sh
TIME_EXEC_MS() {
local t_start
local t_end
t_start=$(date +%s%N)
"$@" > /dev/null
local ret=$?
t_end=$(date +%s%N)
local t_elapsed=$(( (t_end - t_start) / 1000000 )) # ms
echo "${t_elapsed}"
return $ret
}
```
Just replace redirection if you need to see the output. I also created a REPEAT function to measure multiple runs if needed!

If you're on Linux, you can just run: `time python3 prog.py`. For a Python script approach, you can use this snippet:
```python
import time

start = time.perf_counter()
# your code here
end = time.perf_counter()

elapsed_ms = (end - start) * 1000
print(f"Elapsed: {elapsed_ms:.3f} ms")
```
For PowerShell, just use: `(Measure-Command { python your_script.py }).TotalMilliseconds`. For CMD, try this method:
```cmd
set start=%TIME%
python your_script.py
set end=%TIME%
echo Start: %start%
echo End: %end%
```

You can simply prepend `time` to your command if you're using a bash shell to measure the execution time. Check out the manual for more details: https://www.man7.org/linux/man-pages/man1/time.1.html.

The `time` command gives you various time metrics like elapsed, user, and system time, but keep in mind it doesn't show milliseconds directly.

You’ve got the `time` command available in bash, or you can use `/usr/bin/time` for a normal command. If you're coding in Python, the `timeit` module is also a solid option.