Get a bash script to run node.js [duplicate]

Question

I have a node.js file that accepts an integer arg.

I'm trying to write a bash script that looks for number of available cores and launches main.js for each available core.

For 1 core it should call:

node main.js 3000 &

For 2 cores:

node main.js 3000 &
node main.js 30001 &

And so on...

This is my bash script:

#!/bin/bash
numCores=`getconf _NPROCESSORS_ONLN`
i=0
j=3000
while [ $i < $numCores ]
do
    j=$($j+$i)
    node /myApp/main.js $j &
    i=$($i+1)
done

When I try to run it, I get this error:

bash launchnode.sh
launchnode.sh: line 5: 2: No such file or directory

main.js and launchnode.sh are in the same directory.

Any help?

Answer 1

The error is here:

while [ $i < $numCores ]

In bash < is for input redirection. [ is an alias for the test command, and test 0 < 2 means "send input from the file named 2 to the command test 0.

Instead, use test's -lt option for a less-than comparison. Also, don't forget to quote your variables:

while [ "$i" -lt "$numCores" ]

Or, if you're only targeting bash, you can use arithmetic expansion:

while (( i < numCores ))

You also need to use double parentheses on subsequent lines for arithmetic:

i=$(($j+$i))