[SOLVED] How to pass elements of two arrays to a parallel command with :::

Issue

I'm trying to run several python commands in parallel with the parallel command.

I tried playing around with the parallel command but it didn't perform as what I expected

Here's my shell script

arr_1=(a.log b.log c.log d.log)
arr_2=(a.json b.json c.json d.json)
parallel --halt 2 echo "{1} {2}" ::: "${arr_1[@]}" ::: ${arr_2{@}}

What I expected is:

a.log a.json
b.log b.json
c.log c.json
d.log d.json

But what I got was:

a.log a.json
b.log b.json
c.log c.json
d.log d.json
a.log a.json
b.log b.json
c.log c.json
d.log d.json
a.log a.json
b.log b.json
c.log c.json
d.log d.json
a.log a.json
b.log b.json
c.log c.json
d.log d.json

It looks like the shell script ran the command 16 times.

My guess is I didn't pass the two lists correctly, but I'm not sure about it.

Solution

You are looking for :::+:

parallel --halt 2 echo "{1} {2}" ::: "${arr_1[@]}" :::+ ${arr_2[@]}

Available since 20160422.

Answered By - Ole Tange