Linux – tail does not provide output in bash scripts

I’ve written a bash script to filter the “tail” output, and that’s the whole command

 tail -f /var/log/asterisk/messages | awk 'match($12, /[^0-9]91([0-9]{10})@default/, a) {print a[1]}'

Works fine in the CLI, but not in a bash script:

 #!/bin/bash

phonenumber=$(tail -f /var/log/asterisk/messages | awk 'match($12, /[^0-9]91([0-9]{10})@default/, a) {print a[1]}')
 echo "$phonenumber >> test.log"

It doesn’t output anything, (2135551234, is the expected output string) I’ve tried writing to a log file and only writing standard output but none of them work.

I’ve tried writing scripts using “cat” instead of “tail” and it works great. But I don’t want to dump the output of the entire file, so “tail” is used.

I’ve also tried using ‘tee’ but to no avail

The ultimate goal of this script is to send the phone number entering the PBX to a serial device to another system and use as a CID.

Thank you in advance for all your help

Try this :

phonenumber=$(tail -f /var/log/asterisk/messages | awk 'match($12, /[^0-9]91([0-9]{10})@default/, a) {print a[1]; exit}')

Your version doesn’t work because tail -f and awk are in an infinite loop. Adding exit to the awk script terminates the loop when the first phone number is found. awk immediately exits and puts its output into a variable, and tail -f gets a SIGPIPE signal when trying to write the next line to the pipe, which causes it to exit.