On Tue, Jul 21, 2009 at 8:42 PM, Lynn Kerby <l...@kerbit.net> wrote: > > Thanks, I hadn't read the Open Group test command doc. However, I find the > doc inconsistent on this matter when read in its entirety. > > For starters, POSIX doesn't allow for the use of '-a' as a unary operator > (according to the RATIONALE section this is because mere humans will be > confused and should use '-e' instead). In that context, the parsing of 3 > arguments to test could proceed on the assumption that any '-a' option in > the middle would be an attempt to perform a binary operation. The GNU bash > and test command do support the historical '-a' unary operator usage as a > unary operator, so its hard to justify this behavior as POSIX conformant > IMO. It might be, but it is pretty clearly wrong.
It justifies that bash does the posixly correct thing in returning always true for "test ! -a foo" > So if I'm reading that corrrectly, the '!' operator is supposed to have a > higher precedence than the '-a' operator in complex expressions. Simply > adding a "-a 1" to the expression (resulting in " ! -a file -a 1") causes a > different parsing behavior. It seems that the 3 argument processing rules > for the test command violate this by having the negation test ordered after > binary primaries. The rules for 2 and 4 argument parsing clearly handle > negation first. > > I still consider this a bug, since this is caused by an ambiguity (at some > level) in a non-POSIX defined operator. Blaming it on a POSIX defined > argument processing rule doesn't really apply here. Whatever the > disposition, I'm going to be modifying this bunch of scripts (inherited) to > use the '-e' unary operator for existence tests. > This "inversion of priorities" with 3 arguments is documented in man bash. (note that posix doesn't even define what test should do with more than 4 arguments, I find better to not use -a at all and to chain several test command with && or ||, I also find this more readable, some people prefer the ksh/bash [[ keyword which allows you to use && rather than -a)
