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Any @command{awk} variable can be set by including a variable assignment among the arguments on the command line when @command{awk} is invoked (see section Other Command-Line Arguments). Such an assignment has the following form:
variable=text
With it, a variable is set either at the beginning of the @command{awk} run or in between input files. When the assignment is preceded with the @option{-v} option, as in the following:
-v variable=text
the variable is set at the very beginning, even before the
BEGIN rules are run. The @option{-v} option and its assignment
must precede all the file name arguments, as well as the program text.
(See section Command-Line Options, for more information about
the @option{-v} option.)
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 four. 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 two, so that the
second field is printed in lines from `BBS-list':
$ awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list
-| 15
-| 24
...
-| 555-5553
-| 555-3412
...
Command-line arguments are made available for explicit examination by
the @command{awk} program in an array named ARGV
(see section Using ARGC and ARGV).
@command{awk} processes the values of command-line assignments for escape
sequences
(d.c.)
(see section Escape Sequences).
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