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Programming with awk

Output to files

You can print output to files instead of to the standard output by using the > and >> redirection operators. For example, the following program invoked on the file countries prints all lines where the population (third field) is bigger than 100 into a file called bigpop, and all other lines into a file called smallpop:

   $3 > 100   { print $1, $3 >"bigpop" }
   $3 <= 100  { print $1, $3 >"smallpop" }
Notice that the filenames have to be quoted; without quotes, bigpop and smallpop are merely uninitialized variables. If the output filenames were created by an expression, they would also have to be enclosed in parentheses:
   $4 ~ /North America/ { print $1 > ("tmp" FILENAME) }
because the > operator has higher precedence than concatenation; without parentheses, the concatenation of tmp and FILENAME would not work.


NOTE: 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.


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