How to use Parallel and sequential execution of bash scripts in unix

Question

I have 3 shell scripts a.sh, b.sh and c.sh. the scripts a.sh and b.sh are to be run parallely and script c.sh should only run if a.sh and b.sh are run successfully ( with exit code 0).

Below is my code. The parallel execution is working fine but sequential execution of c.sh is out of order. It is executing after completion of a.sh and b.sh even if both the scripts are not returning exit codes 0. Below is the code used.

#!/bin/sh

A.sh &

B.sh &

wait &&

C.sh

How this can be changed to meet my requirement?

What is the return of the last ID? Is it possible that A.sh or B.sh returned a non-zero value. Have you tried removing the "&&". Then C.sh will always be run — teambob
– teambob, Commented Mar 8, 2022 at 5:29
According to the POSIX standard, "If the wait utility is invoked with no operands, it shall wait until all process IDs known to the invoking shell have terminated and exit with a zero exit status" (my emphasis). Therefore, you need to wait for each separately to get the background processes' exit statuses. — Gordon Davisson
– Gordon Davisson, Commented Mar 8, 2022 at 7:53

Wargamer-Senpai · Accepted Answer · 2022-03-08 07:45:36Z

2

    #!/bin/bash
    ./a.sh & a=$!
    ./b.sh & b=$!
    
    if wait "$a" && wait "$b"; then
      ./c.sh
    fi

Hey i did some testing, in my a.sh i had an exit 255, and in my b.sh i had an exit 0, only if both had an exitcode of 0 it executed c.sh.

edited Mar 8, 2022 at 7:45

answered Mar 8, 2022 at 6:41

Wargamer-Senpai

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2 Comments

tripleee Over a year ago

You could simplify to just if wait "$a" && wait "$b"; then...

Wargamer-Senpai Over a year ago

@tripleee yes looks cleaner 👍

yassir ait el aizzi · Accepted Answer · 2022-03-08 05:25:36Z

-1

you can try this :

.....
wait &&
    if [ -z "the scripts a.sh or any commande u need  " ] 
    then
       #do something
       C.sh
    fi

answered Mar 8, 2022 at 5:25

yassir ait el aizzi

723 bronze badges

6 Comments

neelima reddy Over a year ago

Should I use wait && in the beginning??

yassir ait el aizzi Over a year ago

#!/bin/sh A.sh & B.sh & wait && if [ -z "the scripts a.sh or any commande u need " ] then #do something C.sh fi

yassir ait el aizzi Over a year ago

just replace : C.sh with : if [ -z "the scripts a.sh or any commande u need " ] then #do something C.sh fi

user18098820 Over a year ago

If one of the scripts a or b takes longer will c still be run?

neelima reddy Over a year ago

@yassir ait ek aizzi thank you...but, why is the if loop being used there, the purpose?

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