Re: /dev/tcp

Eli the Bearded <*@eli.users.panix.com> writes:
> What system(s) have /dev/tcp/* natively?

Quite possibly none.

>   $ man bash
>   [...]
>   REDIRECTION
>   [...]
>        Bash handles several filenames specially when they are used in
>        redirections,  as described  in the  following table.   If the
>        operating  system on  which  bash is  running  provides  these
>        special files, bash will use them;  other wise it will emulate
>        them internally with the behavior described below.
>   [...]
>               /dev/tcp/host/port
> 		  If  host  is a valid  hostname or Internet address,
> 		  and port is an integer port number or service name,
> 		  bash attempts to open the corresponding TCP socket.
>
> I don't see it on the various systems I have handy (Debian 13, Amazon
> Linux 2023, Mac OS 15.7.x, NetBSD 10.1, Android 14).

The documentation is wrong, at least based on the Bash 5.2.21 source in
Ubuntu. If a filename matches /dev/tcp/*/* then it will call socket &
connect, whatever exists in the local OS. The behaviour can be disabled
at build time but I see nothing that queries the target platform’s
capabilities.

> is it a plan9 thing?

I wondered that, but based on https://9p.io/sys/doc/net/net.html, no.
Plan 9 has /net/tcp but it doesn’t behave like Bash’s /dev/tcp special
case.

Solaris (and other SYSV) has a /dev/tcp but that also does not behave
like the Bash special case, it just provides you with a handle on the
TLI provider for TCP, in case you like gratuitous incompatibility.

-- 
https://www.greenend.org.uk/rjk/