John Wenker <[EMAIL PROTECTED]> wrote: > The following construct _always_ evaluates true, regardless of > whether the file exists or not. > > if [ ! -a file ]; then > echo "This line always prints no matter what." > else > echo "This line never prints." > fi
-a can act as a prefix unary operator, or an infix binary "and" operator. When it appears as the second of three arguments (not counting "]") in a test, it's treated as a binary operator, even if the first argument is "!". So in this case, "!" is test, and as a single string it's only tested for non-emptiness, and so is considered true. Likewise for "file". Since both subtests are true, the combined "and" test is also true. There are a few different ways to get the behavior you want. You could use "[ ! \( -a file \) ]" or "! [ -a file ]", although those are not portable to some other shells. (The behavior of a test is generally more predictable when there are fewer arguments, so I'd go with the second of those two, since it pulls the "!" outside the test and leaves only two arguments for the test to examine.) You could also remove "!" and switch your "then" and "else" clauses, which works with any shell. paul _______________________________________________ Bug-bash mailing list Bug-bash@gnu.org http://lists.gnu.org/mailman/listinfo/bug-bash
