source: vendor/bash/3.1-p17/examples/scripts.v2/pages

#! /bin/bash
#
# original from:
# @(#) pages.sh 1.0 92/09/26
# 92/09/05 John H. DuBois III (jhdiii@armory.com)
# 92/09/26 Added help
#
# conversion to bash v2 syntax by Chet Ramey

Usage="$0 [-h] [-n lines/page] page-ranges [file ...]"

usage()
{
        echo "$Usage" 1>&2
}

phelp()
{
echo "$0: print selected pages.
Usage: $Usage

If no file names are given, the standard input is read.

The input is grouped into pages and a selected subset of them is printed.
Formfeeds are acted on correctly.

If the output device does automatic line wrap, lines that longer than
the width of the output device will result in incorrect output.
The first non-option argument is a list of pages to print.

Pages are given as a list of ranges separated by commas.
A range is either one number, two numbers separted by a dash,
or one number followed by a dash.  A range consisting of one
number followed by a dash extends to the end of the document.

Options: 
-n sets the number of lines per page to n.  The default is 66."
}

while getopts "n:h" opt; do
        case "$opt" in
        n)      LinesPerPage=$OPTARG;;
        h)      phelp; exit 0;;
        *)      usage; exit 2;;
        esac
done

shift $(($OPTIND - 1))

if [ $# -eq 0 ]; then
    echo $0: no page ranges given. 1>&2
    usage
    exit 1
fi

PageList=$1
shift

gawk "
BEGIN {
    PageList = \"$PageList\"; LinesPerPage = \"$LinesPerPage\""'
    if (LinesPerPage == "")
        LinesPerPage = 66
    else
        if (LinesPerPage !~ "[1-9][0-9]*")
            ErrExit("Bad value for lines per page: " LinesPerPage)
    LinesPerPage += 0
    NumRanges = split(PageList,Ranges,",")
    for (i = 1; i <= NumRanges; i++) {
        if ((StartRange = EndRange = Ranges[i]) !~ "^[0-9]+(-([0-9]+)?)?$")
            ErrExit("Bad range \"" StartRange "\"")
        sub("-.*","",StartRange)
        sub(".*-","",EndRange)
        if (EndRange == "")
            EndRange = 2 ^ 30
        # Force StartRange and EndRange to be numeric values
        if ((StartRange += 0) == 0 || (EndRange += 0) == 0)
            ErrExit("Invalid page number \"0\" in range " Ranges[i])
        if (StartRange > EndRange)
            ErrExit("Start page comes after end page in range " Ranges[i])
        TmpRangeStarts[i] = StartRange
        TmpRangeEnds[i] = EndRange
    }

    # Sort ranges
    qsort(TmpRangeStarts,k)
    RangeEnds[0] = 0
    for (i = 1; i <= NumRanges; i++) {
        RangeEnds[i] = TmpRangeEnds[k[i]]
        if ((RangeStarts[i] = TmpRangeStarts[k[i]]) <= RangeEnds[i - 1])
            ErrExit("Overlapping ranges: " Ranges[k[i]] "," Ranges[k[i - 1]])
    }

    RangeNum = LineNum = PageNum = 1
    InRange = In(PageNum,RangeStarts[RangeNum],RangeEnds[RangeNum])
    FS = "\014"
}

{
    if (LineNum > LinesPerPage)
        NewPage()
    if (InRange)
        printf "%s",$1
    # Deal with formfeeds
    for (i = 2; i <= NF; i++) {
        if (InRange)
            printf "\014"
        NewPage()
        if (InRange)
            printf "%s",$i
    }
    if (InRange)
        print ""
    LineNum++
}

function NewPage() {
    PageNum++
    LineNum = 1
    # At the start of each page, check whether we are in a print range
    WereInRange = InRange
    InRange = In(PageNum,RangeStarts[RangeNum],RangeEnds[RangeNum])
    # If last page was in range and we no longer are, move to next range
    if (WereInRange && !InRange && ++RangeNum > NumRanges)
        exit
}

function In(a,Min,Max) {
    return (Min <= a && a <= Max)
}

function ErrExit(S) {
    print S > "/dev/stderr"
    Err = 1
    exit 1
}

# Arr is an array of values with arbitrary indices.
# Array k is returned with numeric indices 1..n.
# The values in k are the indices of array arr, 
# ordered so that if array arr is stepped through
# in the order arr[k[1]] .. arr[k[n]], it will be stepped
# through in order of the values of its elements.
# The return value is the number of elements in the array (n).
function qsort(arr,k,  ArrInd,end) {
    end = 0
    for (ArrInd in arr)
        k[++end] = ArrInd;
    qsortseg(arr,k,1,end);
    return end
}

function qsortseg(arr,k,start,end,  left,right,sepval,tmp,tmpe,tmps) {
    # handle two-element case explicitely for a tiny speedup
    if ((end - start) == 1) {
        if (arr[tmps = k[start]] > arr[tmpe = k[end]]) {
            k[start] = tmpe
            k[end] = tmps
        }
        return
    }
    left = start;
    right = end;
    sepval = arr[k[int((left + right) / 2)]]
    # Make every element <= sepval be to the left of every element > sepval
    while (left < right) {
        while (arr[k[left]] < sepval)
            left++
        while (arr[k[right]] > sepval)
            right--
        if (left < right) {
            tmp = k[left]
            k[left++] = k[right]
            k[right--] = tmp 
        }
    }
    if (left == right)
        if (arr[k[left]] < sepval)
            left++
        else
            right--
    if (start < right)
        qsortseg(arr,k,start,right)
    if (left < end)
        qsortseg(arr,k,left,end)
}
' "$@"