Re: test && test --> test -a

[Tim Van Holder]

> For what it's worth, autoconf says the following.  (Oh, but is this
> saying POSIX doesn't specify -a and -o at all, or only that it doesn't
> specify their precedence?)

Draft 6 of the new POSIX standard lists -a, -o and parens as XSI
extensions.  It also has this to say:

Scripts should be careful when dealing with user-supplied input that
could be confused with primaries and operators. Unless the application
writer knows all the cases that produce input to the script, invocations
like:

        test "$1" −a "$2"

should be written as:

        test "$1" && test "$2"

to avoid problems if a user supplied values such as $1 set to ’!’ and $2 set to 
the null string.
That is, in cases where maximal portability is of concern, replace:

        test expr1 −a expr2

with:

        test expr1 && test expr2

and replace:

        test expr1 −o expr2

with:

        test expr1 || test expr2

but note that, in test, −a has higher precedence than −o while "&&" and "||" 
have equal
precedence in the shell.

Parentheses or braces can be used in the shell command language to effect 
grouping.

Parentheses must be escaped when using sh; for example:

        test \( expr1 −a expr2 \) −o expr3

This command is not always portable outside XSI-conformant systems. The 
following form can
be used instead: 

        ( test expr1 && test expr2 ) || test expr3