Command to get time in milliseconds

Nano is 10⁻⁹ and milli 10⁻³. Hence, we can use the three first characters of nanoseconds to get the milliseconds:

date +%s%3N

From man date:

%N nanoseconds (000000000..999999999)

%s seconds since 1970-01-01 00:00:00 UTC

Source: Server Fault's How do I get the current Unix time in milliseconds in Bash?.

date +%s%N returns the number of seconds + current nanoseconds.

Therefore, echo $(($(date +%s%N)/1000000)) is what you need.

Example:

$ echo $(($(date +%s%N)/1000000))
1535546718115

date +%s returns the number of seconds since the epoch, if that's useful.

date +"%T.%N" returns the current time with nanoseconds.
```
06:46:41.431857000
```
date +"%T.%6N" returns the current time with nanoseconds rounded to the first 6 digits, which is microseconds.
```
06:47:07.183172
```
date +"%T.%3N" returns the current time with nanoseconds rounded to the first 3 digits, which is milliseconds.
```
06:47:42.773
```

In general, every field of the date command's format can be given an optional field width.

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