Given a directed graph and two specified nodes a, b succeed if node a is reachable from node b.

reachable.gvpr

#!/usr/bin/env gvpr -f
#
# Given a directed graph and two specified nodes a, b succeed if
# node a is reachable from node b.
# The program exits with success (0) if a path is found and failure (1)
# if a path isn't found.
#
# Example invocation:
# gvpr -f reachable.gvpr -a sourcename -a targetname file.dot && echo yes
#
#  Copyright 2019 Diomidis Spinellis
#
#  Licensed under the Apache License, Version 2.0 (the "License");
#  you may not use this file except in compliance with the License.
#  You may obtain a copy of the License at
#
#       http://www.apache.org/licenses/LICENSE-2.0
#
#  Unless required by applicable law or agreed to in writing, software
#  distributed under the License is distributed on an "AS IS" BASIS,
#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#  See the License for the specific language governing permissions and
#  limitations under the License.
#
#

BEG_G {
	$tvtype = TV_fwd;
	$tvroot = node($, ARGV[0]);
}

# Stop after this DFS; succeed if node matches specified one
N [$tvroot = NULL; $.name == ARGV[1]] {
	exit(0);
}

END_G {
	exit(1);
}