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You can print output into files, instead of to the standard output, using the ``>'' and ``>>'' redirection operators. For example, if you invoke the following program on the file countries, awk prints all lines where the population (third field) is bigger than 100 into a file called bigpop, and all other lines into smallpop:
$3 > 100 { print $1, $3 >"bigpop" }
$3 <= 100 { print $1, $3 >"smallpop" }
Notice that the filenames must be quoted; without quotes,
bigpop and smallpop are uninitialized
variables. If the output filenames are created by an expression,
they also must be enclosed in parentheses:
$4 ~ /North America/ { print $1 > ("tmp" FILENAME) }
This is because the > operator has higher precedence than
concatenation; without parentheses, the concatenation of
tmp and FILENAME does not work.
Note that files are opened once in an awk program. If
> is used to open a file, its original contents are
overwritten. But if >> is used to open a file, its
contents are preserved and the output is appended to the
file. Once the file has been opened, the two operators have the same
effect.