gawk: One-shot
1.1.1 One-Shot Throwaway 'awk' Programs
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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, to
start '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 'awk'
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 
Very Simple, we'll see examples of
several short, self-contained programs.
Info Catalog
gawk: Running gawk
gawk: Read Terminal