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Let's imagine I have a client and a server on the same machine, and I'd like to script some interaction between them.

I would really like a shell script to -

  1. Start server
  2. Put server in the background
  3. Start client
  4. (wait for client to do whatever it does)
  5. Stop server

I can do most of that already, like this -

./server &
./client

But that leaves server running after the script finishes which, apart from anything else, is very untidy.

What can I do?

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2 Answers 2

up vote 3 down vote accepted

You can use bash job control:

#!/bin/bash

./server &
./client
kill %1

Be sure to put the #!/bin/bash at the beginning of the script so that bash is used to execute the script (I'm not sure if job control is supported in sh, please correct me if it does).

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Thanks! That's exactly what I needed. –  Jez Jul 15 '11 at 15:57
    
No problem! Glad to help! –  Wuffers Jul 15 '11 at 15:59

You can achieve the same result with standard POSIX sh. In sh, when you spawn a process in the background using '&', the PID of the process is stored in the special variable $!. So:

#!/bin/sh
./server &
./client
kill $!

For more complex situations you might want to save the pid:

#!/bin/sh
./server &
serverpid=$!
# ... lots of other stuff
kill $serverpid
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