Re: POSIX on $()

2009-04-23, 09:18(+00), Daniel Chicayban Bastos:
(*) POSIX $()

POSIX's ``Shell & Utilities'' on section ``2.6 Word Expansions'' states

The '$' character is used to introduce parameter expansion, command
substitution, or arithmetic evaluation. If an unquoted '$' is
followed by a character that is either not numeric, [not]
the name of one of the special parameters (see Special
Parameters), [not] a valid first character of a variable
name, [not] a left curly brace ( '{' ) or a left
parenthesis, the result is unspecified.

So, is it the case that

#!/bin/sh
tmp=$(tempfile)

is implementation dependent?

It's true the wording is unclear, I've added a few [not] above
to help clarify.

But applying a bit of common sense, $ is followed by (, so it is
specified, it is a command substitution. What is unspecified as
per POSIX, is what happens when the file starts with "#!" or the
output of "tempfile" as that's not a command specified by POSIX.

[...]
When I say ``man sh,'' I really am reading bash's manual page. What do
you advise if my intention to write POSIX's /bin/sh conformant
programs? For instance, what documentation should I read, even if I
can't wholly rely on it?

bash is a POSIX conformant shell when called as sh. Its manual
describes bash, not the POSIX sh syntax which is a subset of the
syntax recognised by bash. Just like gcc is a C compiler, don't
expect to know how to write portable C code by reading gcc
manual. If you want to learn how to write conformant *scripts*,
read the POSIX specification.

--
Stéphane
.

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