Shell Programming and Scripting

#!/bin/bash
#counter.sh
N=${1:-100}
start=0

# First create counter.txt file with 0 as a start.
touch counter.txt
echo $start > counter.txt
echo "Start value: $start"

USAGE="usage: bash $0 #N# [-s]"
if [ $# -gt 2 ]; then
	echo "$USAGE"
	exit 1
elif [ $# -eq 2 ]; then
	synchronized=true
fi

# create 2*N (parallel) processes:
if [[ $synchronized ]]; then
	echo "SYNchronized:"
	# This for loop is the crux of the counter.sh script:
	for (( i = 0; i < $N; i++ )); do
		(       # Aren't brackets ( and ) enough for parallelism?
		bash inc.sh $i	-s   # switch name (-s) is arbitrary; enough to have 2 args
		bash dec.sh $(($i+1)) -s
		)
	done

else
	echo "A-SYNchronized:"
	for (( i = 0; i < N; i++ )); do
		(
		bash inc.sh $i	
		bash dec.sh $(($i+1))
		)
	done
fi

final=$(cat counter.txt)
echo "Final value: $final"

#!/bin/bash
#dec.sh (inc.sh has a plus (+)instead of minus)
if [ $# -eq 2 ]; then
	lockfile -1 dec.lock
fi

number=$(cat counter.txt)
echo -n "Dec $1: $number -> "
number=$(($number - 1)) # minus is plus (+) in inc.sh
echo $number > counter.txt
echo "$number"

if [ $# -eq 2 ]; then
	rm -f dec.lock
fi

courteous@courteous-P5K ~/Documents/test $ bash counter.sh 5 -s
Start value: 0
SYNchronized:
Inc 0: 0 -> 1
Dec 1: 1 -> 0
Inc 1: 0 -> 1
Dec 2: 1 -> 0
Inc 2: 0 -> 1
Dec 3: 1 -> 0
Inc 3: 0 -> 1
Dec 4: 1 -> 0
Inc 4: 0 -> 1
Dec 5: 1 -> 0
Final value: 0