On 27th of February, Heikki Linnakangas committed patch:
Add support for piping COPY to/from an external program. This includes backend "COPY TO/FROM PROGRAM '...'" syntax, and corresponding psql \copy syntax. Like with reading/writing files, the backend version is superuser-only, and in the psql version, the program is run in the client. In the passing, the psql \copy STDIN/STDOUT syntax is subtly changed: if you the stdin/stdout is quoted, it's now interpreted as a filename. For example, "\copy foo from 'stdin'" now reads from a file called 'stdin', not from standard input. Before this, there was no way to specify a filename called stdin, stdout, pstdin or pstdout. This creates a new function in pgport, wait_result_to_str(), which can be used to convert the exit status of a process, as returned by wait(3), to a human-readable string. Etsuro Fujita, reviewed by Amit Kapila.