input redirection in subshell before command results in error

[Andrew Brown]

Configuration Information [Automatically generated, do not change]:
Machine: i386
OS: netbsdelf
Compiler: cc
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='i386' 
-DCONF_OSTYPE='netbsdelf' -DCONF_MACHTYPE='i386--netbsdelf' -DCONF_VENDOR='' 
-DSHELL  -DHAVE_CONFIG_H  -I.  -I. -I./include -I./lib -I/usr/pkg/include -O2 
-I/usr/pkg/include
uname output: NetBSD this 2.0E NetBSD 2.0E (THAT) #328: Thu May 20 11:15:27 EDT 
2004  andrew@this:/usr/src/sys/arch/i386/compile/THAT i386
Machine Type: i386--netbsdelf

Bash Version: 2.05b
Patch Level: 0
Release Status: release

Description:

bash can do:

    diff -u <(postconf -d) <(postconf)

which is neat, yet most sh-type shells cannot do that.  the way that
works in most other sh-type shells that i've found (where /dev/fd
exists) is:

    postconf | ( 3<&0 ( postconf -d | diff - /dev/fd/3 ) )

this works in netbsd's sh, solaris's /bin/sh (and solaris's /sbin/sh
and /usr/xpg4/bin/sh), and in irix's sh, at the very least, along with
ksh and zsh.  the error given is:

    bash: -c: line 1: syntax error near unexpected token `('
    bash: -c: line 1: `postconf | ( 3<&0 ( postconf -d | diff - /dev/fd/3 ) )'

Repeat-By:

    postconf | ( 3<&0 ( postconf -d | diff - /dev/fd/3 ) )