close() on pipe command does not return exit status

[juster]

An undocumented feature of other awks is to have the close() builtin function return the exit status of the process which was opened by the pipe. The close() builtin for goawk always returns -1 for output pipes and always returns 0 for input pipes.

Example

$ goawk 'BEGIN { print|"exit 1"; print close("exit 1") }'
-1
$ goawk 'BEGIN { "exit 1"|getline; print close("exit 1") }'
0

Portability?

Different awks also have various implementations. The same example above was run for ...

1. the "one-true" Lucent copyright awk
2. GNU gawk
3. plan9 from userspace awk
4. Mac OS awk

Variant	Input/Output Pipe	Behavior
one-true / mac os	both	Value is 256 (1 << 8)
gawk	both	Value is 1
plan9	both	Use of the value of close() is illegal

edit: Removed duplicate rows. I also remembered how the wait() result shifts the exit code.

[benhoyt]

Interesting! Linking the GAWK docs on this for reference. For comparison, POSIX just says "If the close was successful, the function shall return zero; otherwise, it shall return non-zero."

[juster]

Ah nice! Those linked docs explain plan9 awk's behavior:

In many older versions of Unix awk, the close() function is actually a statement. (d.c.) It is a syntax error to try and use the return value from close():

It complains about an illegal statement.

But yeah this is definitely an undocumented easter egg!