$ printf -v now '%(%T)T'
$ echo "$now"
12:42:47

Syntax

• printf '%(dateFmt)T' # dateFmt can be any format string that strftime recognizes
• printf '%(dateFmt)T' -1 # -1 represents the current time (default for no argument)
• printf '%(dateFmt)T' -2 # -2 represents the time the shell was invoked

Remarks

Using printf -v foo '%(...)T' is identical to foo=$(date +'...') and saves a fork for the call to the external program date.