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Suppose we have a txt file file.txt with each line is a python script e.g. python a1.py python a2.py python a3.py

What does the following command is really doing ?

cat file.txt | xargs -n 1 -P $NUM_CPUS bash -c

  • this forum is not the best place to ask if this is a homework....first step, read man xargs....then read man bash for the -c flag... – mazs Oct 20 '17 at 13:50
1

Elucidation:

cat file.txt | xargs -n 1 -P $NUM_CPUS bash -c
  • cat file.txt - concatenate the file file.txt contents passed to next program in pipeline

  • xargs -n 1 - accept 1 argument from the STDIN(previous command output) at a time

  • -P $NUM_CPUS - run up to $NUM_CPUS processes at a time (one input line for each process invocation)

  • bash -c - the command executed with current argument

1

Assuming $NUM_CPUS contains an integer, then the command will start at most that many parallel non-interactive bash shells (that's what -P does). Each shell will run one line from the input file (due to -n 1).

The cat command is not needed:

xargs -n 1 -P "$NUM_CPUS" bash -c <file.txt

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