:
##########################################################################
# Title      :	fieldchange - print only lines where field changed
# Author     :	Heiner Steven <heiner.steven@odn.de>
# Date       :	1996-01-23
# Requires   :	
# Category   :	Text Utilities
# SCCS-Id.   :	@(#) fieldchange	1.3 13/01/20
##########################################################################
# Description
#
##########################################################################

PN=`basename "$0"`			# program name
VER='1.3'

: ${AWK:=nawk}

usage () {
    echo >&2 "$PN - print only lines where field changed, $VER (stv '96)
usage: $PN [-d delim] [-f field] [-f field ...] file [...]
    -d: delimiter (default: whitespace)
    -f: field number (starting with field 1)

If no field is given, the first field is watched for changes."
    exit 1
}

msg () {
    for i
    do echo "$PN: $i" >&2
    done
}

fatal () { msg "$@"; exit 1; }

#set -- `getopt hf: "$@"`
Fields=
Delim=
while [ $# -gt 0 ]
do
    case "$1" in
	-d)
	    Delim=$2; shift;;
	-f)	
	    for i in $2
	    do
	        expr "$i" + 0 > /dev/null 2>&1 ||
		    fatal "No field number: $i"
	    done
	    Fields="${Fields:+$Fields }$2"
	    shift;;
	--)	shift; break;;
	-h)	usage;;
	-*)	usage;;
	*)	break;;			# First file name
    esac
    shift
done

: ${Fields:=1}

$AWK ${Delim:+-F"$Delim"} '
    BEGIN {
	k = split ("'"$Fields"'", C)
	for ( i=1; i<=k; i++ ) Cols [C [i]] = "yes"
    }
    {
	if ( NF != OldNF ) PrintLine = 1; else PrintLine = 0
	for ( i in Cols ) {
	    if ( Old [i] != $i ) {
		PrintLine = 1
		Old [i] = $i
	    }
	}
	if ( PrintLine ) print
	OldNF = NF
    }
' "$@"