Ubuntu – How to run multiple commands in parallel and see output from both

You could use a script. Save the following as run-parallel.sh, and make it executable (chmod +x run-parallel.sh):

#! /bin/bash
trap "pkill -P $$; kill -INT $$" INT

while read n
do
    "$@" &
done < <(seq 1000)
wait

Explanation:

• trap ... INT sets a command to be run when the SIGINT signal is received (which is the signal generated when you press CtrlC).
• $$ is the PID of the current process (that is, of the script itself). pkill -P $$ kills those processes whose parent process i the script.
• It is convention that a program which catches SIGINT kill itself using SIGINT once it has tidied up. Hence, the kill -INT $$.
• seq 1000 generates numbers from 1 to 1000.
• The while loop runs the command provided as arguments to the script once for each number from seq, and sends them to the background.
• Then we wait until all of the background processes finish executing.

Run it thus:

./run-parallel.sh php process.php

Meet GNU parallel (sudo apt install parallel):

GNU parallel is a shell tool for executing jobs in parallel using one or more computers. (…) [It] makes sure output from the commands is the same output as you would get had you run the commands sequentially. (man parallel)

In your case with repeating arguments you can make use of bash Brace Expansion to easily build the command lines. The basic syntax is parallel COMMAND {} ::: ARGUMENTS, if you want to give each run multiple arguments take care of proper quoting to prevent word splitting, e.g.:

$ parallel echo ./run some args {} ::: {"1 0 "{10,25},"2 0 10"}\ {0.{1,2,5},1}
./run some args 1 0 10 0.1
./run some args 1 0 10 0.2
./run some args 1 0 10 0.5
./run some args 1 0 10 1
./run some args 1 0 25 0.1
./run some args 1 0 25 0.2
./run some args 1 0 25 0.5
./run some args 1 0 25 1
./run some args 2 0 10 0.1
./run some args 2 0 10 0.2
./run some args 2 0 10 0.5
./run some args 2 0 10 1