Filter map and reduc in pure Bash

Functional Bash

#!/usr/bin/env bash

function filter {
	while read line; do
		if [ "$($1 $line)" -ne 0 ]; then
			echo $line
		fi
	done
}

function map {
	while read line; do
		echo "$($1 $line)"
	done
}

function reduce {
	local acc=$2
	while read line; do
		acc="$($1 $acc $line)"
	done
	echo $acc
}

function odd {
	echo $(($1 % 2 == 1))
}

function double {
	echo $(($1 * 2))
}

function sum {
	echo $(($1 + $2))
}

seq 1 5 \
 	| filter odd \
	| map double \
	| reduce sum 0