Answer by Stéphane Chazelas for How to get milliseconds since Unix epoch?

In case anyone is using other shells than bash, ksh93 and zsh have a floating point $SECONDS variable if you do a typeset -F SECONDS which can be handy to measure time with accuracy:

$ typeset -F SECONDS=0$ do-somethingsomething done$ echo "$SECONDS seconds have elapsed"18.3994340000 seconds have elapsed

Since version 4.3.13 (2011) zsh has a $EPOCHREALTIME special floating point variable in the zsh/datetime module:

$ zmodload zsh/datetime$ echo $EPOCHREALTIME1364401642.2725396156$ printf '%d\n' $((EPOCHREALTIME*1000))1364401755993

Note that that's derived from the two integers (for seconds and nanoseconds) returned by clock_gettime(). On most systems, that's more precision than a single C double floating point number can hold, so you'll lose precision when you use it in arithmetic expressions (except for dates in the first few months of 1970).

$ t=$EPOCHREALTIME$ echo $t $((t))1568473231.6078064442 1568473231.6078064

To compute high precision time differences (though I doubt you'd need more than millisecond precision), you may want to use the $epochtime special array instead (which contains the seconds and nanoseconds as two separate elements).

Since version 5.7 (2018) the strftime shell builtin also supports a %N nanosecond format à la GNU date and a %. to specify the precision, so the number of milliseconds since the epoch can also be retrieved with:

zmodload zsh/datetimestrftime %s%3. $epochtime

(or stored in a variable with -s var)