bash sieve of eratosthenes

Dockerfile

FROM alpine:latest

RUN ["apk", "add", "bash"]
COPY "sieve.sh" "$WORKDIR"
ENTRYPOINT ["./sieve.sh"]

sieve.sh

#!/usr/bin/env bash

eratosthenes() {
    tmp_dir="$1"
    n="$2"

    # Only need to search composites up to sqrt(n)
    local max
    max=$(echo "sqrt($n)" | bc)

    # Use files in $tmp_dir to represent a set of composites (starts empty)
    local i
    local j
    seq 2 "$max" | while IFS= read -r i; do
        if [ -e "$tmp_dir/$i" ]; then
            continue
        fi

        seq $(( i * i )) "$i" "$n" | while IFS= read -r j; do
            touch "$tmp_dir/$j"
        done
    done

    seq 2 "$n" | while IFS= read -r i; do
        if ! [ -e "$tmp_dir/$i" ]; then
            echo "$i"
        fi
    done
}

set -uo pipefail

if [ "$#" -lt 1 ]; then
    echo "Usage: $0 N"
    exit 1
fi

N="$1"
TMP_DIR=$(mktemp -d)

# Clean up the temp dir when done
trap 'rm -Rf $TMP_DIR' EXIT

eratosthenes "$TMP_DIR" "$N"