How to derive current date and time and append at the end of each line that contains 'Hello'

Question

I have the following file party.txt that contains something like the following:

Hello Jacky
Hello Peter
Bye Johnson
Hello Willy
Bye Johnny
Hello Mar         


        

Answer 1

To answer the direct question, what you're missing is that date is an external command, and so you need to either invoke it outside of awk and pass it in as a variable (as one of the other answers demonstrates), or invoke it from within awk as a system command either using the system() built-in or a pipe (as another one of the other answers demonstrates).

The reason you see 0 is because the expression date +"%Y-%m-%d" is being interpreted as adding the numeric value of the variable date (which will be 0 as it's not defined) to the numeric value of the string "%Y-%m-%d" (which will be 0 as it's not a valid number).

Answer 2

In gawk only:

$ gawk '/Hello/ {print $0, strftime("%Y-%m-%d");}' party.txt 
Hello Jacky 2019-09-17 
Hello Peter 2019-09-17 
Hello Willy 2019-09-17 
Hello Mary 2019-09-17 
Hello Wendy 2019-09-17