Why does bash report syntax errors when my C News scripts use a
redirection before a subshell command?
Why does bash report syntax errors when my C News scripts use a
redirection before a subshell command?
The actual command in question is something like
< file ( command )
According to the grammar given in the POSIX.2 standard, this construct
is, in fact, a syntax error. Redirections may only precede `simple
commands'. A subshell construct such as the above is one of the shell's
`compound commands'. A redirection may only follow a compound command.
This affects the mechanical transformation of commands that use `cat'
to pipe a file into a command (a favorite Useless-Use-Of-Cat topic on
comp.unix.shell). While most commands of the form
cat file | command
can be converted to `< file command', shell control structures such as
loops and subshells require `command < file'.
The file CWRU/sh-redir-hack in the bash-2.05a distribution is an
(unofficial) patch to parse.y that will modify the grammar to
support this construct. It will not apply with `patch'; you must
modify parse.y by hand. Note that if you apply this, you must
recompile with -DREDIRECTION_HACK. This introduces a large
number of reduce/reduce conflicts into the shell grammar.
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