PREFACE
Computer users spend a lot
of
time doing simple, mechanical
data
manipula-
tion - changing the format of data, checking its validity, finding items with
some property, adding up numbers, printing reports, and the like. All
of
these
jobs ought to be mechanized, but it's a real nuisance to have to write a special-
purpose program in a standard language like C or Pascal each time such a task
comes up.
Awk
is
a programming language
that
makes it possible to handle such tasks
with very short programs, often only one or two lines long. An awk program
is
a sequence
of
patterns and actions that tell what to look for in the input data
and what to do when it's found. Awk searches a set of files for lines matched
by any
of
the patterns; when a matching line
is
found, the corresponding action
is
performed. A pattern can select lines
by
combinations
of
regular expressions
and comparison operations
on
strings, numbers, fields, variables, and array ele-
ments. Actions may perform arbitrary processing
on
selected lines; the action
language looks like C but there are
no
declarations, and strings and numbers
are built-in
data
types.
Awk scans the input files and splits each input line into fields automatically.
Because so many things are automatic - input, field splitting, storage manage-
ment, initialization - awk programs are usually much smaller than they would
be in a more conventional language. Thus one common use
of
awk
is
for the
kind of
data
manipulation suggested above. Programs, a line or two long, are
composed
at
the keyboard, run once, then discarded. In effect, awk
is
a
general-purpose programmable tool that can reprace a host
of
specialized tools
or programs.
The same brevity of expression and convenience
of
operations make awk
valuable for prototyping larger programs.
One starts with a
few
lines, then
refines the program until it does the desired job, experimenting with designs by
trying alternatives quickly. Since programs are short, it's easy to get started,
and easy to
start
over when experience suggests a different direction. And it's
straightforward to translate an awk program into another language once the
design
is
right.
iii
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