A simple implementation of the quick sort algorithm.

quicksort.sh

#!/bin/bash

# A basic quick sort implementation. 
# It takes a list of numbers (separated by spaces),
# and it prints them out in ascending order.
quicksort() {

    # The list passed in.
    local LIST=($@)

    # What's the length?
    local LENGTH=${#LIST[@]}

    # What's the middle number?
    local PIVOT=${LIST[$(( $LENGTH / 2 ))]}

    # Values in the list that are lesser than the pivot will go here:
    local LESSER=()

    # Values in the list that are greater than the pivot will go here:
    local GREATER=()

    # Values in the list that are equal to the pivot will go here:
    local EQUAL=()

    # If we have more than one item in the list,
    # we can process it.
    if [[ $LENGTH -gt 1 ]]; then

        # Sort each item in the list into
        # $LESSER, $GREATER, and $EQUAL lists.
        for N in ${LIST[@]}
        do
            if [[ $N -lt $PIVOT ]]; then
                LESSER=( ${LESSER[@]} $N )
            elif [[ $N -gt $PIVOT ]]; then
                GREATER=( ${GREATER[@]} $N )
            else
                EQUAL=( ${EQUAL[@]} $N )
            fi
        done

        # Now sort each sub-list (if it has any members in it).
        if [[ ${#LESSER[@]} -gt 0 ]]; then
            quicksort ${LESSER[@]}
        fi
        if [[ ${#EQUAL[@]} -gt 0 ]]; then
            quicksort ${EQUAL[@]}
        fi
        if [[ ${#GREATER[@]} -gt 0 ]]; then
            quicksort ${GREATER[@]}
        fi

    # If there's just one item in the list, we can print it.
    else
        printf "${LIST[@]} "
    fi

}

# Example. 
# Here's an unsorted list 
LIST="10 2 5 3 6 7 0 4 8 13"

# Sort it with quicksort, and store the output in $SORTED_LIST
SORTED_LIST=`quicksort ${LIST[@]}`

# Print 'er out.
echo $SORTED_LIST

exit 0

Simple and broken, if you have a duplicated element in the list it will loop forever