#!/bin/sh -u
#
# Replace text between two lines denoted by regexps.
#	- Cameron Simpson <cs@zip.com.au> 20sep95
#

: ${TMPDIR:=/tmp}

cmd=`basename "$0"`
usage="Usage: $cmd -f from -t to [-i input] [-o output] replacement-files...
	-f from	Start line marked specified by regexp \"from\".
	-t to	Start line marked specified by regexp \"to\".
	-i input Take input from \"input\", default stdin.
	-o output Write result to \"output\", default stdout."

input=-
output=-
from=
to=

badopts=

while [ $# -gt 0 ]
do
  case $1 in
    -f)	from=$2; shift ;;
    -t)	to=$2; shift ;;
    -i)	input=$2; shift ;;
    -o)	output=$2; shift ;;
    --)	shift; break ;;
    -?*)echo "$cmd: unrecognised option: $1" >&2
	badopts=1 ;;
    *)	break ;;
  esac
  shift
done

[ -n "$from" ] || { echo "$cmd: missing -f option" >&2; badopts=1; }
[ -n "$to" ] || { echo "$cmd: missing -t option" >&2; badopts=1; }
[ $# = 0 ] && { echo "$cmd: missing replacement-files" >&2; badopts=1; }

[ $badopts ] && { echo "$usage" >&2; exit 2; }

tmp=$TMPDIR/$cmd.$$
front=$tmp.a
back=$tmp.b

case $from in
    */*)	from=`printf '%s\n' "$from"|sed 's|/|\\\\/|g'` ;;
esac
case $to in
    */*)	to=`printf '%s\n' "$to"|sed 's|/|\\\\/|g'` ;;
esac

ok=1

trap 'rm -f "$front" "$back"' 0
trap 'rm -f "$front" "$back"; exit 1' 1 2 13 15

exec 3<&0	# save stdin

[ "x$input" = x- ] || exec <"$input"

# read the whole input file and grab the top and bottom bits
# this lets us use the same file for input and output
sed -n "1,/$from/w $front
        /$to/,\$w $back" || ok=

if [ $ok ]
then
    [ "x$output" = x- ] || exec >"$output"
    for file in "$front" "$@" "$back"
    do
      case $file in
	-)	cat <&3 ;;
	/*)	cat "$file" ;;
	*)	cat "./$file" ;;
      esac || ok=
    done
fi

[ $ok ] && exit 0
exit 1