I process files found by `ls` as

```
ls /folder/ | parallel -j20 ./command {}

```

but I need to pass the job number as well. I tried

```
ls /folder/ | parallel -j20 ./command {1} {2} ::: {1..20}
ls /folder/ | parallel -j20 ./command {} {} ::: {1..20}

```

but it does not work. I also tried `{#}` for passing the job number.