Easy shell script (korn) question

[Jeanine Kone]

I am writing a shell script and in the middle of it I have two commands that I want to run at the same time. I dont want the scipt to continue until BOTH comamnds have completed.

I know I can put an & at the end of the first command so the second one kicks off right away and runs at the same time, but how do I make the shell script wait for the next command if the second one finishes first?

Thanks!

[vtpaulson]

Hi,

Use wait command. wait command will wait untill the previous background command finishes. See the man page for more info.

Reg,

Paulson

[James R. Ferguson]

Hi Jeanine:

Consider this:

./mytask1 &
T1=$! #...capture the pid of mytask1...
./mytask2
if [ $? -eq 0 ]; then
echo "task2 completedok"
fi
wait T1 #...wait for mytask1...
if [ $? -eq 0 ]; then
echo "task1 completedok"
fi

...JRF...

[A. Clay Stephenson · Accepted solution]

Hi:

By far the easist method is you don't care about the order of execution is:

cmd1.sh &
cmd2.sh &
wait

wait will then pause the parent shell until all child processes have completed.

A variation on this is:
(cmd1.sh; cmd2.sh) &
cmd3.sh
wait

In this case cmd2.sh does not start until cmd1.sh has finished. cmd3.sh run concurrently with cmd1.sh,cmd2.sh. Control does not return until all child processes have finished.

Regards, Clay

[A. Clay Stephenson]

Hi:

By far the easist method is you don't care about the order of execution is:

cmd1.sh &
cmd2.sh &
wait

wait will then pause the parent shell until all child processes have completed.

A variation on this is:
(cmd1.sh; cmd2.sh) &
cmd3.sh &
# I missed this ampersand in the prior posting
wait

In this case cmd2.sh does not start until cmd1.sh has finished. cmd3.sh run concurrently with cmd1.sh,cmd2.sh. Control does not return until all child processes have finished.

Regards, Clay

[Magdi KAMAL]

Hi Jeanine,

example :

cmd1 &
cmd2 &

wait

cmd3

cmd3 will execute only and only if cmd1 AND cmd2 finish ( both of then )

Note : wait is a synchronizing point.


Magdi