Question 2 (argfile input syntax)

[paralleluser]

Friends,

Question 2:
There are a multitude of ways to give GNU parallel arguments contained in a 
file.

1. cat argfile | parallel
2. parallel < argfile
3. parallel :::: argfile
4. parallel ::: `cat argfile`
5. parallel -a argfile

Am I missing any from this list?


I am curious as to which you use when and why.  I think the answer is beyond 
"personal preference".  For example, I would ...

Use #1 if you plan to do additional pipe work before parallel, for example:
  cat argfile | grep xyz | parallel

Use #5 if you are going to use "-a" multiple times so you can refer to {1} and 
{2} etc
  parallel -a argfile1 -a argfile2  command {1} {2}

I don't see a good reason to use #4

I think #2 and #3 seem about the same.  What advantage is there to use either 
of them over #1?

Much thanks...