How can I kill a process when a specific string is seen on standard error?

Question

I need to start a process, lets say foo. I would like to see the stdout/stderr as normal, but grep the stderr for string bar. Once

Answer 1

Use Expect to Monitor Standard Error

Expect is designed for taking actions based on output from a process. The simplest solution is to simply let Expect start the process, then exit when it sees the expected output. For example:

expect -c 'set msg {Saw "foo" on stderr. Exiting process.}
           spawn /bin/bash -c "echo foo >&2; sleep 10"
           expect "foo" { puts $msg; exit }'

If the spawned process ends normally (e.g. before "foo" is seen), then the Expect script will exit, too.