Assigning Variables on the Command Line
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   You can set any `awk' variable by including a "variable assignment"
among the arguments on the command line when you invoke `awk' (
see Invoking `awk': Command Line.).  Such an assignment has this form:

     VARIABLE=TEXT

With it, you can set a variable either at the beginning of the `awk'
run or in between input files.

   If you precede the assignment with the `-v' option, like this:

     -v VARIABLE=TEXT

then the variable is set at the very beginning, before even the `BEGIN'
rules are run.  The `-v' option and its assignment must precede all the
file name arguments, as well as the program text.

   Otherwise, the variable assignment is performed at a time determined
by its position among the input file arguments: after the processing of
the preceding input file argument.  For example:

     awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list

prints the value of field number `n' for all input records.  Before the
first file is read, the command line sets the variable `n' equal to 4.
This causes the fourth field to be printed in lines from the file
`inventory-shipped'.  After the first file has finished, but before the
second file is started, `n' is set to 2, so that the second field is
printed in lines from `BBS-list'.

   Command line arguments are made available for explicit examination by
the `awk' program in an array named `ARGV' (*note Built-in
Variables::.).

   `awk' processes the values of command line assignments for escape
sequences (see Constant Expressions: Constants.).