The awk language has evolved over the years. Full details are
provided in section The Evolution of the awk Language.
The language described in this book
is often referred to as "new awk."
Because of this, many systems have multiple
versions of awk.
Some systems have an awk utility that implements the
original version of the awk language, and a nawk utility
for the new version. Others have an oawk for the "old awk"
language, and plain awk for the new one. Still others only
have one version, usually the new one.(2)
All in all, this makes it difficult for you to know which version of
awk you should run when writing your programs. The best advice
we can give here is to check your local documentation. Look for awk,
oawk, and nawk, as well as for gawk. Chances are, you
will have some version of new awk on your system, and that is what
you should use when running your programs. (Of course, if you're reading
this book, chances are good that you have gawk!)
Throughout this book, whenever we refer to a language feature
that should be available in any complete implementation of POSIX awk,
we simply use the term awk. When referring to a feature that is
specific to the GNU implementation, we use the term gawk.
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