tail没有在bash脚本中提供输出

Question

i have written a bash script that will filter 'tail' output, which the entire command

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

works fine from the CLI but not when placed in the 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"

which doesn't output anything, (2135551234, is the expected output string) i have tried writing to the log file and writing just the stdout but neither work.

i have tried the script using 'cat' instead of 'tail' and that works fine. but i dont want to dump the output of the entire file, hence the use of 'tail'.

I have also tried using 'tee' but to no avail

the end goal of this script with be to send the phone number as it comes into the PBX to a serial device to another system and used as the CID.

thanks for all your help in advance

Answer 1

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 exits immediately and its output is put into the variable, and tail -f gets a SIGPIPE signal when it tries to write the next line to the pipe, which causes it to exit.