On Sat, 7 Dec 2013, Daniel Barnes wrote:
> There's a few issues with this that causes this behavior:
>
> The way "or" works, it waits until the first command has been executed, then
> moves on to the second. The "if" only seems to be taking the first command,
> and the "or" is actually being executed inside the block:
>
> if false;
> or true;
> echo yes;
> ..
>
>
> So, first `false` is being evaluated to.. false, then it is skipping right to
> the "else" block. Therefore, the output is "no".
Correct.
> In the case you would want to make sure the "or" applies in the first
> statement, you should use parentheses:
eek. You should use blocks, not command substitutions.
> set myTest (false; or true)
> echo $status # 0
> set myTest (false; or false)
> echo $status # 1
> set myTest (true; or false) # note: the second "false" is not evaluated
> because the true was already true.
> echo $status # 0
>
> if $myTest; #...
The argument to your conditional here is the output of 'true; or false',
not the return value. You could do `set myTest (true; or false); if
$status`: see https://github.com/fish-shell/fish-shell/issues/547 to see
why this works.
> Also, one other thing to mention: the `test` command has an -o (or) and -a
> (and) switch, made for using these operators (though I can't figure out how
> they work, I seem to be receiving weird results and thus can't provide and
> example... test (false) -o (false) has an exit status of 0 for me). Maybe it
> will help for what you're doing, it seems to be more aimed at making tests for
> things like that.
Your test command compares the output of the command substitution, not the
return value. `false` produces no output, so the command substitution
expands to nothing; thus you are effectively running `test -o`, which (per
the POSIX standard [1]) is true.
The `-o` and `-a` operators are for comparing expressions which are valid
test expressions in their own right. For example, you could do `test -d
/etc -a -r /etc` to see if /etc/ is a directory that you can probably read
from.
David Adam
zanc...@ucc.gu.uwa.edu.au
[1]: http://www.unix.com/man-page/POSIX/1/test/
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