Re: BUG #18926: PostgreSQL 17.5 produces malformed binary COPY output (`GPOCYP` instead of `PGCOPY`) across platform

PG Bug reporting form <noreply(at)postgresql(dot)org> writes:
> I'm encountering a bug in PostgreSQL 17.5 where a `COPY ... TO STDOUT WITH
> (FORMAT binary)` operation produces malformed output: the file begins with
> `GPOCYP` instead of the expected `PGCOPY`. This behavior occurs consistently
> across environments, including:

Works as expected for me, on macOS and RHEL8:

$ psql -q -f mini_test.sql >output.bin
$ hexdump -C output.bin | head
00000000 50 47 43 4f 50 59 0a ff 0d 0a 00 00 00 00 00 00 |PGCOPY..........|
00000010 00 00 00 00 01 00 00 00 04 00 00 00 01 ff ff |...............|
0000001f

I think your version of hexdump is regarding the input as 2-byte LSB-first
integers. (Maybe you replaced it with some "helpful" alias?)

You might try double-checking the file with some other tool, eg od:

$ od -c output.bin | head
0000000 P G C O P Y \n 377 \r \n \0 \0 \0 \0 \0 \0
0000020 \0 \0 \0 \0 001 \0 \0 \0 004 \0 \0 \0 001 377 377
0000037

regards, tom lane