如何使用shell脚本运行依赖于正在运行的进程的第二个进程？

Question

I want to do an automation for 2 processes using shell script. I have 2 programs, a is a workload, b is a CPU profiler to profile the cpu when a is running.

Previously, I run these programs manually, by opening 2 terminals. First, run a in the first terminal, then in another terminal, I get the process ID of a , and finally run ./b [pid-of-a] . This has caused me to miss the profiling of the first few seconds of process a .

I tried:

./a &
pid=$! & 
./b pid

But it does not work the way I wanted. It runs b first and returns an error because the PID of a does not exist. I can't use && as well because it will wait a to finish first before b starts which is not the way I want.

What modification should I do to my code regarding such dependency?

Answer 1

Don't set pid in the background, and remember to put a $ when you want to expand it:

./a & 
pid=$!
./b "$pid"

Or just

./a &  
./b $!

Answer 2

Write a bash script which will check for ProcessA using pgrep and gets its pid

 #!/bin/sh while true do pid=`pgrep -f processA` if [ ! -z $pid ] then ./processB $pid break fi done