Flatten an arbitrarily-nested array of integers

flatten.bash

#!/bin/bash
pad_response_in_brackets() {
        echo -n "["
        cat < /dev/stdin
        echo "]"
}

strip_brackets() {
        gsed 's/\[//g' | gsed 's/\]//g'
}

flatten() {
        list=$* # Interpret the list of ints as a string

        echo -n $list | strip_brackets | pad_response_in_brackets
}


## Unit Tests
# For each test, we run an action and "grep" for its expected output. Should one
# of the actions produce an incorrect output, grep will fail and the tests will
# stop.
set -e # Exit immediately if one of the tests fails

### test pad_response_in_brackets
echo -n "x" | pad_response_in_brackets | grep [x]

### test strip_brackets
echo -n "[1,[2,[3]]]" | strip_brackets | grep "1,2,3"

### test flatten
flatten [1,2,3]                        | grep [1,2,3]
flatten [1,2,[3]]                      | grep [1,2,3]
flatten [1,[2,[3]]]                    | grep [1,2,3]
flatten [[1,2,[3]],4]                  | grep [1,2,3,4]