perl - How to write hostfile in Slurm script

Question

Currently I am doing following

 #!/bin/bash -l
 #SBATCH --nodes=2
 #SBATCH --ntasks-per-node=4

 scontrol show hostname $SLURM_JOB_NODELIST | perl -ne 'chomb; print "$_" x4' > myhostfile

This generates the following myhostfile

 compute-0
 compute-0
 compute-0
 compute-0
 compute-1
 compute-1
 compute-1
 compute-1

I would like to have the following outcome

 compute-0
 compute-1
 compute-0
 compute-1
 compute-0
 compute-1
 compute-0
 compute-1

So that we alternate between all specified nodes

question from:https://stackoverflow.com/questions/65844698/how-to-write-hostfile-in-slurm-script

Answer 1

You can do it like this:

$ perl -e 'print +(<>) x 4'

This removes the -n loop from your code, and instead reads the entire STDIN in one go. We need the parentheses () to get the read operator into list context, so it reads all lines at once. The + tells the perl interpreter that the parentheses are a list, and not part of the print (as print()). Finally the repeat operator x in list context repeats the entire list.

$ cat foo
0
1
$ cat foo | perl -e 'print +(<>) x 4'
0
1
0
1
0
1
0
1