Once you are familiar with
awk, you will often type in simple
programs the moment you want to use them. Then you can write the
program as the first argument of the
awk command, like this:
awk 'program' input-file1 input-file2 …
where program consists of a series of patterns and actions, as described earlier.
This command format instructs the shell, or command interpreter,
awk and use the program to process records in the
input file(s). There are single quotes around program so
the shell won’t interpret any
awk characters as special shell
characters. The quotes also cause the shell to treat all of program as
a single argument for
awk, and allow program to be more
than one line long.
This format is also useful for running short or medium-sized
programs from shell scripts, because it avoids the need for a separate
file for the
awk program. A self-contained shell script is more
reliable because there are no other files to misplace.
Later in this chapter, in Some Simple Examples, we’ll see examples of several short, self-contained programs.