want to add milliseconds in time stamp of console output using gawk bash

Question

I am using following snippet to add timestamp to console output

command | gawk '{ print strftime("[%Y-%m-%d %H:%M:%S]"), $0 }'  

how to add milliseconds to it?

Answer 1

Why not a simple bash solution? You can read each line and prepend a timestamp using the date command, e.g.

command | while read -r line; do printf "%s %s\n" "$(date +'%F %T.%03N')" "$line"; done

Example Use/Output

Sample lines:

$ cat dat/captnjack.txt
This is a tale
Of Captain Jack Sparrow
A Pirate So Brave
On the Seven Seas.

Timestamped output:

$ cat dat/captnjack.txt | 
while read line; do printf "%s %s\n" "$(date +'%F %T.%03N')" "$line"; done
2022-06-24 00:45:28.030 This is a tale
2022-06-24 00:45:28.031 Of Captain Jack Sparrow
2022-06-24 00:45:28.033 A Pirate So Brave
2022-06-24 00:45:28.035 On the Seven Seas.

(note: thank you @jhnc for the GNU date %03N specifier)

With bash you can also use process substitution to feed the timestamp loop, e.g.

while read -r line; do 
  printf "%s %s\n" "$(date +'%F %T.%03N')" "$line"
done < <(command)