I am pleased to announce the availability of a test version of gawk.
This version uses a byte-code execution engine, and most importantly,
it includes a debugger that works at the level of awk statements! The
distribution is available at
http://www.skeeve.com/gawk/gawk-3.1.7-bc-d.tar.gz.
This version is the same as 3.1.7, but with a new execution engine and
a debugging version of gawk named, rather imaginatively, "dgawk".
There is a story here. Circa 2003, a gentleman by the name of Jon Haque
developed the byte-code execution engine and debugger, in the context
of a development gawk version, somewhere between 3.1.3 and 3.1.4.
I never integrated the changes as they were massive and I was busy,
and I wasn't able to review them.
The changes languished, and Jon disappeared.
Last fall, Stephen Davies, one of my portability team members, agreed to
take on the task of bringing the code into the present. With modest help
from me, he succeeded. We then went through additional work to get this
version portable to some of the more esoteric systems that gawk supports
(64 bit Linux, z/OS and VMS).
I thought it was ready for release at the end of December, until another
one of my testers found a severe memory leak in the byte code version.
It was a bear to track down, and once again Stephen came through.
The debugger uses the readline library, and it is purposely similar
to GDB. There is only minimal documentation on the debugger; I'd love
to have someone volunteer to write a chapter for the gawk manual that
explains it fully.
Example
./dgawk -f ../share/awk/round.awk
dgawk> help
backtrace backtrace [N]
break break [[filename:]N|function]
clear clear [[filename :]N|function]
continue continue [COUNT] - continue program being debugged.
delete delete [breakpoints] [range]
disable disable [breakpoints] [range]
display display var - print value of variable
down down [N] - move N frames down the stack.
dump dump [filename] - dump bytecode.
enable enable [once|del] [breakpoints] [range]
finish finish - execute until selected stack frame returns.
frame frame [N] - select and print stack frame number N.
help help - print list of commands.
ignore ignore N COUNT - set ignore-count of breakpoint
info info topic
list list [-|+|[filename:]lineno|function|range]
next next [COUNT] - step program
nexti nexti [COUNT] - step one instruction
print print var [var] - print value of a variable
quit quit - exit debugger.
return return [value]
run run - start executing program.
set set var = value - assign value to a scalar
step step [COUNT] - step program
stepi stepi [COUNT] - step one instruction
tbreak tbreak [[filename:]N|function]
trace trace on|off - print instruction
undisplay undisplay [N] - remove variable(s)
until until [[filename:]N|function]
unwatch unwatch [N] - remove variable(s) from watch list.
up up [N] - move N frames up the stack.
watch watch var - set a watchpoint for a variable.
Here is the debugger printing a function definition:
dgawk> list
1 # round.awk --- do normal rounding
2 #
3 # Arnold Robbins, arnold@skeeve.com, Public Domain
4 # August, 1996
5
6 function round(x, ival, aval, fraction)
7 {
8 ival = int(x) # integer part, int() truncates
9
10 # see if fractional part
11 if (ival == x) # no fraction
12 return ival # ensure no decimals
13
14 if (x < 0) {
15 aval = -x # absolute value
