On 11/18/24 6:31 AM, Klüver, Tibor wrote:
Bash Version: 5.2 Patch Level: 15 Release Status: releaseDescription: Built-in `[ -a ... ]` returns true when false, negation with `!` is also very strange. `[[` is not affected, neither is `/bin/[`.
`test' uses an algorithm based on the number of arguments supplied. The man page specifies the precedence and behavior for each number of arguments.
Repeat-By:
* touch file
* [ -a file ] && echo exists => exists
Two arguments: -a is a unary primary with two arguments, and file exists.
* [ ! -a file ] && echo exists => exists
Three arguments: -a is a binary primary, both arguments are non-empty strings; the test succeeds.
* [ ! ! -a file ] && echo exists => (nothing)
Four arguments: the first argument is `!' so this is the negation of the three argument test; the test fails.
* [ ! ! ! -a file ] && echo exists => (nothing)
Five arguments: operator-precedence parsing using the historical test algorithm. It's basically `not-not-not' -a file, which is the same as `not' -a file, which fails.
* [ ! ! ! ! -a file ] && echo exists => exists
Six arguments: operator-precedence parsing again.
Same as previous, just add another `not' at the beginning, so it's
the result of the binary `-a file' test, which succeeds.
This is the reason POSIX recommends not using more than two or three
argument tests and using the shell's && and || operators to compose
more complicated tests.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU c...@case.edu http://tiswww.cwru.edu/~chet/
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