Parallel processing in bash, collecting all resulting STDOUT from children

gistfile1.txt

#!/bin/bash

# trap handler to cleanly shutdown all children if aborted (i.e. ^C is invoked)
function abort {
	cd - > /dev/null

	# ignore the SIGTERM that is about to be issued
	trap '' SIGTERM
	echo "Signalling shutdown to all children..."
	kill 0

	echo "Waiting on all children to finish..."
	wait

	exit 1
}

# usage message
if [ $# -lt 2 ]; then
	echo "Usage: $(basename $0) <file> <children>" >&2
	exit 1
fi

# number of children argument
if ! [[ $2 =~ ^[0-9]+$ ]]; then
	echo "Second argument must be number of parallel children" >&2
	exit 1
fi
CHILDREN=$2

# input file argument (for demo purposes)
INPUTFILE="$(readlink -m "$1")"
if [ ! -r "$INPUTFILE" ]; then
	echo "Could not read input file '$INPUTFILE'" >&2
	exit 1
fi

# calculate how to split the input file up per-child (for demo purposes)
echo "Processing '$INPUTFILE'..."
FILELEN=$(wc -l "$INPUTFILE" | cut -d ' ' -f 1)
if [ $FILELEN -eq 0 ]; then
	echo "File length is 0, nothing to do."
	exit 1
fi

echo "File length is $FILELEN"
if [ $FILELEN -lt $CHILDREN ]; then
	CHILDREN=$FILELEN
	echo "Limiting children count to $FILELEN"
fi

let PERCHILD=FILELEN/CHILDREN
echo "$PERCHILD to be ran per each child"

# can customise to pipe output into something else or a variable even
OUTCMD='tee combined.out'

# parallel children processing
trap abort SIGINT
{
	for i in $(seq 1 $CHILDREN); do
		let HEAD=PERCHILD*i
		(
			echo "Spawned child $i" >&2
			for FILELINE in $(head $INPUTFILE -n $HEAD | tail -n $PERCHILD); do
				echo "[INFO] Child $i processing '$FILELINE'" >&2
        
				sleep 0.2 # in reality some real processing would happen here...
				if [ $? -ne 0 ]; then
					echo "[WARN] Child $i failed to process '$FILELINE'" >&2
				else
					echo "Child $i processed '$FILELINE'"
				fi
			done
			exit
		) &
	done
} | eval "$OUTCMD" || abort

# cleanup at end
echo "Waiting on children..."
wait
exit 0
# end