how to wait for first command to finish

Question

I am writing a script in bash  which is calling two bash scripts internally  Where first script includes different tests which runs in background and second script print results of first script   When I run these two scripts one after other  sometimes  second script get executed before first script ends Which prints wrong results    I am running both scripts with source command  Any better suggestions   source       st new sh -basedir  STRESS PATH -instances  INSTANCES  source       results sh

User · Answer

Make sure that st new sh does something at the end what you can recognize  like touch  tmp st new tmp when you remove the file first and always start one instance of st new sh   Then make a polling loop  First sleep the normal time you think you should wait  and wait short time in every loop  This will result in something like  max retry 20 retry 0 sleep 10   Minimum time for st new sh to finish while     retry  -lt   max retry     do    if   -f  tmp st new tmp    then       break   call results sh outside loop    else          retry   retry   1          sleep 1    fi done if   -f  tmp st new tmp    then    source       results sh     rm -f  tmp st new tmp else    echo Something wrong with st new sh fi

User · Answer

Shell scripts  no matter how they are executed  execute one command after the other  So your code will execute results sh after the last command of st new sh has finished   Now there is a special command which messes this up   amp   cmd  amp    means   Start a new background process and execute cmd in it  After starting the background process  immediately continue with the next command in the script    That means  amp  doesn t wait for cmd to do it s work  My guess is that st new sh contains such a command  If that is the case  then you need to  modify the script   cmd  amp  BACK PID      This puts the process ID  PID  of the new background process in the variable BACK PID  You can then wait for it to end   while kill -0  BACK PID   do     echo  Process is still active         sleep 1       You can add a timeout here if you want done   or  if you don t want any special handling output simply  wait  BACK PID   Note that some programs automatically start a background process when you run them  even if you omit the  amp   Check the documentation  they often have an option to write their PID to a file or you can run them in the foreground with an option and then use the shell s  amp  command instead to get the PID

[linux] how to wait for first command to finish?

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