Passing second argument to GNU parallel while feeding ls

Question

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.

Answer 1

The {#} replacement string should be exactly what you need here. For example, given

$ ls
 file1  'file2 with spaces'  'file3'$'\n''with'$'\n''newlines'   file4   file5

then

parallel --null echo {#} {} ::: *
1 file1
2 file2 with spaces
3 file3
with
newlines
4 file4
5 file5

or, if you have enough files to exceed the ARG_MAX limit you could use

printf '%s\0' * | parallel --null echo {#} {}

Answer 2

It is unclear to me what you want to do. Maybe one of these?

ls /folder/ | parallel -j20 ./command {1} {2} :::: - ::: {1..20}
ls /folder/ | parallel -j20 ./command {1} {2} :::: - :::+ {1..20}
ls /folder/ | parallel -j20 ./command {1} {#}
ls /folder/ | parallel -j20 ./command {1} {%}