Arnold Robbins and I are good friends. We were introduced
in 1990
by circumstances—and our favorite programming language, AWK.
The circumstances started a couple of years
earlier. I was working at a new job and noticed an unplugged
Unix computer sitting in the corner. No one knew how to use it,
and neither did I. However,
a couple of days later, it was running, and
I was root and the one-and-only user.
That day, I began the transition from statistician to Unix programmer.
On one of many trips to the library or bookstore in search of
books on Unix, I found the gray AWK book, a.k.a.
Alfred V. Aho, Brian W. Kernighan, and
Peter J. Weinberger’s The AWK Programming Language (Addison-Wesley,
1988). awk’s simple programming paradigm—find a pattern in the
input and then perform an action—often reduced complex or tedious
data manipulations to a few lines of code. I was excited to try my
hand at programming in AWK.
Alas, the awk on my computer was a limited version of the
language described in the gray book. I discovered that my computer
had “old awk” and the book described
“new awk.”
I learned that this was typical; the old version refused to step
aside or relinquish its name. If a system had a new awk, it was
invariably called nawk, and few systems had it.
The best way to get a new awk was to ftp the source code for
gawk from prep.ai.mit.edu. gawk was a version of
new awk written by David Trueman and Arnold, and available under
the GNU General Public License.
(Incidentally,
it’s no longer difficult to find a new awk. gawk ships with
GNU/Linux, and you can download binaries or source code for almost
any system; my wife uses gawk on her VMS box.)
My Unix system started out unplugged from the wall; it certainly was not
plugged into a network. So, oblivious to the existence of gawk
and the Unix community in general, and desiring a new awk, I wrote
my own, called mawk.
Before I was finished, I knew about gawk,
but it was too late to stop, so I eventually posted
to a comp.sources newsgroup.
A few days after my posting, I got a friendly email
from Arnold introducing
himself. He suggested we share design and algorithms and
attached a draft of the POSIX standard so
that I could update mawk to support language extensions added
after publication of The AWK Programming Language.
Frankly, if our roles had been reversed, I would not have been so open and we probably would have never met. I’m glad we did meet. He is an AWK expert’s AWK expert and a genuinely nice person. Arnold contributes significant amounts of his expertise and time to the Free Software Foundation.
This book is the gawk reference manual, but at its core it
is a book about AWK programming that
will appeal to a wide audience.
It is a definitive reference to the AWK language as defined by the
1987 Bell Laboratories release and codified in the 1992 POSIX Utilities
standard.
On the other hand, the novice AWK programmer can study
a wealth of practical programs that emphasize
the power of AWK’s basic idioms:
data-driven control flow, pattern matching with regular expressions,
and associative arrays.
Those looking for something new can try out gawk’s
interface to network protocols via special /inet files.
The programs in this book make clear that an AWK program is typically much smaller and faster to develop than a counterpart written in C. Consequently, there is often a payoff to prototyping an algorithm or design in AWK to get it running quickly and expose problems early. Often, the interpreted performance is adequate and the AWK prototype becomes the product.
The new pgawk (profiling gawk), produces
program execution counts.
I recently experimented with an algorithm that for
n
lines of input, exhibited
~ C n^2
performance, while
theory predicted
~ C n log n
behavior. A few minutes poring
over the awkprof.out profile pinpointed the problem to
a single line of code. pgawk is a welcome addition to
my programmer’s toolbox.
Arnold has distilled over a decade of experience writing and
using AWK programs, and developing gawk, into this book. If you use
AWK or want to learn how, then read this book.
Michael Brennan
Author of mawk
March 2001