[PATCH (topgit) 1/2] Implement setup_pager just like in git

@@ -243,6 +243,59 @@ do_help()
 	fi
 }
 
+## Pager stuff
+
+# isatty FD
+isatty()
+{
+	tty -s 0<&$1 || return 1
+	return 0
+}
+
+# setup_pager
+# Spawn pager process and redirect the rest of our output to it
+setup_pager()
+{
+	isatty 1 || return 0
+
+	# TG_PAGER = GIT_PAGER | PAGER
+	# http://unix.derkeiler.com/Newsgroups/comp.unix.shell/2004-03/0792.html
+	case ${GIT_PAGER+XXX} in
+	'')
+		case ${PAGER+XXX} in
+		'')
+			# both GIT_PAGER & PAGER unset
+			TG_PAGER=''
+			;;
+		*)
+			TG_PAGER="$PAGER"
+			;;
+		esac
+		;;
+	*)
+		TG_PAGER="$GIT_PAGER"
+		;;
+	esac
+
+	[ -z "$TG_PAGER"  -o  "$TG_PAGER" = "cat" ]  && return 0
+
+
+	# now spawn pager
+	export LESS=${LESS:-FRSX}	# as in pager.c:pager_preexec()
+
+	_pager_fifo="$(mktemp -t tg-pager-fifo.XXXXXX)"
+	rm "$_pager_fifo" && mkfifo -m 600 "$_pager_fifo"
+
+	"$TG_PAGER" < "$_pager_fifo" &
+	exec > "$_pager_fifo"		# dup2(pager_fifo.in, 1)
+
+	# this is needed so e.g. `git diff` will still colorize it's output if
+	# requested in ~/.gitconfig with color.diff=auto
+	export GIT_PAGER_IN_USE=1
+
+	# atexit(close(1); wait pager)
+	trap "exec >&-; rm $_pager_fifo; wait" EXIT
+}
 
 ## Startup