This gist shows an interesting use i've found of background processes and `wait` keyword. I spawn two processes with different duration and then wait for them to finish. The 2 processes run simultaneously and the script finishes once both have finished. It can be useful when you have to deal with long-running processes and want to optimize the t…

test_parallel_processes.sh

#!/bin/bash


# --------------------------------------------
# Here we could define our GLOBAL variables.
#       Using `declare -r` makes the variable read-only (just like a constant in other languages)
# --------------------------------------------
declare -r BOLD='\033[1m';
declare -r NORMAL='\033[0m';



# --------------------------------------------
# This will be the entry point of the script.
#
# This kind of C-like structure allows to define the main code block BEFORE everything else, so that code is more visible and clear
# --------------------------------------------
main () {
        # I use 'printf' over echo because it gives me more control over what can i display.
        #       Passing variables/commands as parameters automatically escapes them
        printf "${BOLD}[%s] START test...${NORMAL}\n\n" "$(date +'%H:%M:%S')";

        time test

        printf "\n";
        printf "${BOLD}[%s] END test...${NORMAL}\n\n" "$(date +'%H:%M:%S')";

        return 0;
}




# --------------------------------------------
# Every other function definition goes here
# --------------------------------------------
function test () {
        printf "[%s] Starting first process (10 sec duration)...\n" "$(date +'%H:%M:%S')";
        sleep 10 &

        printf "[%s] Starting second process (8 sec duration), now in a sub-shell...\n" "$(date +'%H:%M:%S')";
        (sleep 8) &

        printf "[%s] Waiting for all the processes to finish their execution\n\n" "$(date +'%H:%M:%S')";
        wait

        printf "[%s] All child processes has finished execution\n" "$(date +'%H:%M:%S')";
}


# THIS executes the main function. It is placed at the end so that at the time of execution everything is already defined
main "$@"