Kill the running command when expected output is met

I have a command which will do some activity will display message on screen that contains word "continue".
As soon as that word is found, I want to kill that command. I tried below syntax but it is not working.

Command_to_run >> "logfile" 2>&1 &    
    pid=$!
        while ! grep -q "continue"  "$logfile" ; 
         do
           sleep 1
         done
kill -$pid

One method would be to have command_to_run redirect the output to a pipe, and have the pipe closed as soon as the requested output appears in the output.

When the standard output is closed, most commands will exit as soon as they try to write something new to stdout.

Here is an example of how this could be achieved:

File command_to_run:

#!/bin/bash
echo start
seq 2 
echo continue
seq 10
echo end

$ ./command_to_run | tee logfile | awk '1;/continue/{exit}'
start
1
2
continue

Alternatively, if you don't need the output to appear in stdout, you can use grep:

./command_to_run | tee logfile | grep -q continue

$ cat logfile 
start
1
2
continue

It's worth mentioning that the code in the OP almost works as well, it just needs some minor tweaks:

• remove the dollar sign from logfile in the grep command to match the name that is used above
• Use redirection without append to logfile so that continue string is not present from previous execution
• add the end-of-options modifier -- in the kill command so that the negative PID (group) is not evaluated as a signal number.

./command_to_run > "logfile" 2>&1 &    
pid=$!
while ! grep -q "continue"  "logfile" ; 
do
  sleep 1
done
kill -- -$pid

You can use coproc for that

#! /bin/bash

coproc ./command_to_run
until [[ $line =~ continue ]]; do
    read -r -u ${COPROC[0]} line
done
kill $COPROC_PID

if you really want the log file you can write to it inside the loop.