In most implementations of awk, you can only have up to ten files and one pipe open simultaneously. Therefore, POSIX awk provides a close( ) function that allows you to close a file or a pipe. It takes the same expression that opened the pipe or file as an argument. This expression must be identical, character by character, to the one that opened the file or pipe—even whitespace is significant.
In the second form, close one end of either a TCP/IP socket or a two-way pipe to a coprocess. how is a string, either “from” or “to”. Case does not matter.