Howto do floating point compasiosn in an if-statement within a GNU parallel block?

Question

I want to run a batch process in parallel. For this I pipe a list to parallel. When I've an if-statement, that compares two floating point numbers (taken form here), the code doesn't run anymore. How can this be solved.

LIMIT=25

ps | parallel -j2 '   
    echo "Do stuff for {} to determine NUM"    
    NUM=33.3333 # set to demonstrate

    if (( $(echo "$NUM > $LIMIT" | bc -l) )); then
        echo "react..."
    fi

    echo "Do stuff..."
    '

Prints:

Do stuff for \ \ PID\ TTY\ \ \ \ \ \ \ \ \ \ TIME\ CMD to determine NUM
Do stuff...
(standard_in) 2: syntax error
#... snipp

Answer 1

While GNU Parallel is designed to deal correctly with commands spanning multiple lines, I personally find that hard to read. I prefer using a function:

doit() {
  arg="$1"
  echo "Do stuff for $a to determine NUM"    
  NUM=33.3333 # set to demonstrate

  if (( $(echo "$NUM > $LIMIT" | bc -l) )); then
      echo "react..."
  fi

  echo "Do stuff..."
}
export -f doit

LIMIT=25
export LIMIT

ps | parallel -j2 doit

Instead of the exports you can use env_parallel:

ps | env_parallel -j2 doit

If your environment is too big, use env_parallel --session before starting:

#!/bin/bash

env_parallel --session

# Define functions and variables _after_ running --session
doit() {
  [...]
}
LIMIT=25

ps | env_parallel -j2 doit