#! /bin/sh
# subst - substitute strings into files, carefully

PATH=/bin:/usr/bin ; export PATH

case "$1" in
-f)	substs=$2
	shift ; shift
	;;
*)	echo "$0: no substitutions file given" >&2
	exit 2
	;;
esac

# going via a tempfile avoids annoying quoting problems in botched shells
sed -n '/^#/d
s/^\([^	]*\)		*\([^	]*\)$/s#@<\1>@#\2#g/p' $substs >/tmp/sb$$
them="`cat /tmp/sb$$ ; rm -f /tmp/sb$$`"

for f
do
	# first, figure out temporary names
	case "$f"
	in
		*/*)
		dir="`echo $f | sed 's;/[^/]*$;;'`"
		new="$dir/substtmp.new"
		old="$dir/substtmp.old"
		;;

		*)
		new="substtmp.new"
		old="substtmp.old"
		;;
	esac
	echo "$f: " | tr -d '\012'
	rm -f $new $old

	# test existences
	if test ! -f $f
	then
		echo "$0: cannot find \`$f'" >&2
		exit 1
	fi
	if test -r $new
	then
		echo "$0: $new exists, cannot proceed" >&2
		exit 1
	fi
	if test -r $old
	then
		echo "$0: $old exists, cannot proceed" >&2
		exit 1
	fi
	touch $old $new 2>/dev/null
	if test ! -w "$old" -o ! -w "$new"
	then
		rm -f $old $new
		echo "$0: cannot create temporaries $old $new" >&2
		exit 1
	fi

	# generate the new version
	trap "rm -f $new; exit 1" 1 2 15
	# the ''""'' business is more robust against stupid shell implementors
	# than just ""
	sed '/=()<.*>()=/{
		h
		n
		g
		s/.*=()<//
		s/>()=.*//
		'"$them"'
	}' $f >$new

	# substitute new for old, if necessary
	if cmp -s $new $f
	then
		rm -f $new $old
		echo "unchanged"
	else
		mv $f $old || exit 1
		mv $new $f || { mv $old $f ; exit 1 ; }
		rm -f $old
		echo "updated"
	fi
	trap 1 2 15
done