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categories: Papers,Verification,Jul,2009,MikhailA

An AWK Debugger and Assertion Checker

From "AUI - the Debugger and Assertion Checker for the Awk Programming Language" by Mikhail Auguston, Subhankar Banerjee, Manish Mamnani, Ghulam Nabi, Juris Reinfelds, Ugis Sarkans, and Ivan Strnad . Proceedings of the 1996 International Conference on Software Engineering: Education and Practice (SE:EP '96)

Download from LAWKER.


This paper describes the design of Awk User Interface (AUI). AUI is a graphical programming environment for editing, running, testing and debugging of Awk programs. The AUI environment supports tracing of Awk programs, setting breakpoints, and inspection of variable values.

An assertion language to describe relationship between input and output of Awk program is provided. Assertions can be checked after the program run, and if violated, informative and readable messages can be generated. The assertions and debugging rules for the Awk program are written in a separate text file. Assertions are useful not only for testing and debugging but can be considered as a mean for program formal specification and documentation.


The input file contains a list of all states of U.S.A. There are 50 records separated by newlines, one for each of the states. The number of fields in a record is variable. The first field is the name of the state, and the subsequent fields are names of neighbor states. Fields are separated by tabs. For example, the first two records in the database are

Alabama Mississippi Tennessee Georgia Florida 

The task is to color the U.S.A. map in such a way that any two neighboring states are in different colors. We will do it in a greedy manner (without backtracking), assigning to every state the ?rst possible color. The Awk program for this task is the following:

# Greedy map coloring 
BEGIN { FS= "\t"; OFS= "\t" # fields separated by tabs 
		color[0]= "yellow"  # color names 
		color[1]= "blue" 
		color[2]= "red" 
		color[3]= "green" 
		color[4]= "black" 
{ 		i=0 
		while (a[$1,i] ) i++ # find first acceptable color for 
		                     # state $1 
		print $1"\t" color[i] # assign that color 
		for (j=2; j<=NF; j++) a[$j,i]=1	# make that color 
                                            # unacceptable for 
                                            # states $2..$NF 

We can check the correctness of the coloring using the following assertion:

/* Checks the correctness of map coloring - any two neighbor
   states should be colored in different colors */
			(r1.$1 == r2.$1 AND 
 			FOREACH i IN 2..FIELD_NUM(r1) 
				(EXISTS r3: RECORD FROM FILE output 
					(r3.$1 == r1.$i ANDr3.$2!=r2.$2) 
SAY "Map colored correctly" 
ONFAIL  SAY r1.$1 "and" r1.$i "are of the same color" 
        SAY "although they are neighboring states" 
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