Added helpful error messages for erroneous arguments

* Added clarifying comma to help message.

e-Knife/src/main/java/eknife/EKnife.java

@@ -27,9 +27,10 @@ import edg.graph.Node;
 import edg.slicing.ConstrainedAlgorithm;
 import edg.slicing.SlicingAlgorithm;
 import edg.slicing.SlicingCriterion;
-import eknife.config.Config;
 
 import java.io.File;
+import java.util.LinkedList;
+import java.util.List;
 import java.util.Set;
 
 public class EKnife
@@ -113,8 +114,8 @@ public class EKnife
 		help += "  -l,--line   <num>           The line of the slicing criterion\n";
 		help += "  -v,--var    <name>          The name of the slicing criterion (must be a variable)\n";
 		help += "  -n,--occurrence <num>       The occurrence of the slicing criterion in that line\n";
-		help += "  -G --print-graph <file.dot> Exports the graph as a dot file\n";
-		help += "  -G --print-graph <file.pdf> Exports the graph as a PDF file\n";
+		help += "  -G,--print-graph <file.dot> Exports the graph as a dot file\n";
+		help += "  -G,--print-graph <file.pdf> Exports the graph as a PDF file\n";
 		help += "  --help                      Show this message.\n";
 
 		System.out.print(help);
@@ -180,12 +181,26 @@ public class EKnife
 		}
 
 		boolean isValid() {
-			return inputPath != null && new File(inputPath).exists() &&
-					outputFile != null && (outputFile.exists() || outputFile.getAbsoluteFile().getParentFile().isDirectory()) &&
-					file != null &&
-					line > 0 &&
-					name != null && !name.isEmpty() &&
-					occurrence > 0;
+			List<String> errors = new LinkedList<>();
+			if (inputPath == null)
+				errors.add("You must specify a file to analyze with '-i'.");
+			else if (!new File(inputPath).exists())
+				errors.add("The input file you've specified does not exist or isn't readable(" + inputPath + ").");
+			if (outputFile == null)
+				errors.add("You must specify a location for the output with '-o'.");
+			else if (!outputFile.exists() && !outputFile.getAbsoluteFile().getParentFile().isDirectory())
+				errors.add("The output file's parent folder does not exist, or the output folder does not exist.");
+			if (file == null)
+				errors.add("The input file is a folder, so you must specify a the file that contains the slicing criterion with '-f'.");
+			if (line <= 0)
+				errors.add("You must specify a line number greater than 0 with '-l'.");
+			if (name == null || name.isEmpty())
+				errors.add("You must specify a valid variable name with '-v'.");
+			if (occurrence <= 0)
+				errors.add("You must specify an occurrence greater than 0 with '-n'.");
+			for (String error : errors)
+				System.out.println(error);
+			return errors.isEmpty();
 		}
 	}
 }