awk Language ¶awkawk and gawkawkawk ¶The basic function of awk is to search files for lines (or other
units of text) that contain certain patterns. When a line matches one
of the patterns, awk performs specified actions on that line.
awk continues to process input lines in this way until it reaches
the end of the input files.
Programs in awk are different from programs in most other languages,
because awk programs are data driven (i.e., you describe
the data you want to work with and then what to do when you find it).
Most other languages are procedural; you have to describe, in great
detail, every step the program should take. When working with procedural
languages, it is usually much
harder to clearly describe the data your program will process.
For this reason, awk programs are often refreshingly easy to
read and write.
When you run awk, you specify an awk program that
tells awk what to do. The program consists of a series of
rules (it may also contain function definitions,
an advanced feature that we will ignore for now;
see User-Defined Functions). Each rule specifies one
pattern to search for and one action to perform
upon finding the pattern.
Syntactically, a rule consists of a pattern followed by an
action. The action is enclosed in braces to separate it from the
pattern. Newlines usually separate rules. Therefore, an awk
program looks like this:
pattern { action }
pattern { action }
...