BASH SCRIPT: Combining Permutations of Contents in a Directory - linux

Question

I'm currently trying to combine the contents of all .rule files in the rules directory.
For example:
./rules
./numbersFirst.rule
./numbersLast.rule
./lettersFirst.rule
etc.
Each of these files has about 1,000 rules. I need to write a bash script that can output all permutations of each of these rules.
For all the singles, it would just be:
cat rules/*.rule >> ruleSet
Is there any way to do this programmatically and cleverly? For example:
for rule1 in rules/*.rule
do
for rule2 in rules/*.rule
do
if [ $rule1 != $rule 2 ]
then
#read both files and output "$line_rule1 $line_rule2"
#Magic here?
fi
done
done
What about for permutations of 3, 4, ... n files, each with 1,000 lines each? The ideal is to programmatically do this with n files so that I can simple add to the directory and rebuild from this script. Obviously it will be a LOT of combinations!

Answer 1

You can compute cartesian product with GNU parallel if available :
#!/bin/bash
YOUR_DIR="./rules"
ARGS="::: "
NUM=0
for file in $YOUR_DIR/*.rule; do
ARGS="$ARGS $(cat $file | tr "\n" " ") ::: "
NUM=$((NUM+1))
INDEX="$INDEX {$NUM}"
done
if [ ! -z "$ARGS" ]; then
parallel --no-notice -P1 echo $INDEX $ARGS
fi
Or through only recurrence with associative array :
#!/bin/bash
dim=()
YOUR_DIR="./rules"
NUM=0
for file in $YOUR_DIR/*.rule; do
ARGS="$(cat $file | tr "\n" " ")"
dim[$NUM]="$ARGS"
NUM=$((NUM+1))
done
for i in "${!dim[#]}"
do
echo "key : $i"
echo "value: ${dim[$i]}"
done
function iterate {
local index="$2"
if [ "${index}" == "${#dim[#]}" ]; then
for (( i=0; i<=${index}; i++ ))
do
echo -n "${items[$i]} "
done
echo ""
else
for element in ${dim[${index}]}; do
items["${index}"]="${element}"
local it=$((index+1))
iterate items[#] "$it"
done
fi
}
declare -a items=("")
iterate "" 0
You can find a generalization here