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bash/sieve/README.md

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+# Sieve
+
+Use the Sieve of Eratosthenes to find all the primes from 2 up to a given
+number.
+
+The Sieve of Eratosthenes is a simple, ancient algorithm for finding all
+prime numbers up to any given limit. It does so by iteratively marking as
+composite (i.e. not prime) the multiples of each prime, starting with the
+multiples of 2. It does not use any division or remainder operation.
+
+Create your range, starting at two and continuing up to and including the given limit. (i.e. [2, limit])
+
+The algorithm consists of repeating the following over and over:
+
+- take the next available unmarked number in your list (it is prime)
+- mark all the multiples of that number (they are not prime)
+
+Repeat until you have processed each number in your range.
+
+When the algorithm terminates, all the numbers in the list that have not
+been marked are prime.
+
+The wikipedia article has a useful graphic that explains the algorithm:
+https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+
+Notice that this is a very specific algorithm, and the tests don't check
+that you've implemented the algorithm, only that you've come up with the
+correct list of primes. A good first test is to check that you do not use
+division or remainder operations (div, /, mod or % depending on the
+language).
+
+
+Run the tests with:
+
+```bash
+bats sieve_test.sh
+```
+
+After the first test(s) pass, continue by commenting out or removing the
+`[[ $BATS_RUN_SKIPPED == true ]] || skip` 
+annotations prepending other tests.
+
+To run all tests, including the ones with `skip` annotations, run:
+
+```bash
+BATS_RUN_SKIPPED=true bats sieve_test.sh
+```
+
+## Source
+
+Sieve of Eratosthenes at Wikipedia [http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes](http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes)
+
+
+## External utilities
+`Bash` is a language to write "scripts" -- programs that can call
+external tools, such as
+[`sed`](https://www.gnu.org/software/sed/),
+[`awk`](https://www.gnu.org/software/gawk/),
+[`date`](https://www.gnu.org/software/coreutils/manual/html_node/date-invocation.html)
+and even programs written in other programming languages, 
+like [`Python`](https://www.python.org/).
+This track does not restrict the usage of these utilities, and as long
+as your solution is portable between systems and does not require
+installation of third party applications, feel free to use them to solve
+the exercise.
+
+For an extra challenge, if you would like to have a better understanding
+of the language, try to re-implement the solution in pure `Bash`,
+without using any external tools. Note that there are some types of
+problems that bash cannot solve, such as performing floating point
+arithmetic and manipulating dates: for those, you must call out to an
+external tool.
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others
+have completed the exercise.

bash/sieve/sieve.sh

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+#!/usr/bin/env bash
+
+usage() {
+    echo "Usage: ./seave.sh <number>"
+    exit 1
+}
+end=$1
+
+[[ ! "$end" =~ ^[[:digit:]]*$ ]] && usage
+
+declare -a numbers
+
+sep=""
+for (( i=2; i<=end; ++i )); do
+    if [[ ${numbers[$i]} == "" ]]; then
+        echo -n "$sep$i"
+        for (( j=i*2; j<=end; j+=i )); do
+            numbers[$j]=t
+        done
+        sep=" "
+    fi
+done
+echo
+exit 0