[word_eval] Fix shifted slicing of ${@:offset:length}.

[akinomyoga]

This is a quick fix for the third item in #653 (comment). I tried to make the change small, so it might not be so elegant.

Note: dash and mksh fail in test/spec.sh word-split for newly added tests because they don't support ${@:offset:length}.

[andychu]

Oh man I didn't know this -- have you seen it documented anywhere?

This is confusing to me:

$ set -- 1 2 3; echo ${@:2}
2 3
$ a=(1 2 3); echo ${a[@]:2}
3

But apparently zsh agrees with bash! So I guess we should do it... (if multiple shells agree on a behavior I take that as an argument for it.) zsh is usually the one that disagrees the most.

I see what you're doing, but let me think if there's a simpler way...

[andychu]

Wow this is also confusing:

$ set -- 1 2 3; echo ${@};
1 2 3
$ set -- 1 2 3; echo ${@:0};
-bash 1 2 3

You can get more items by adding index 0 !!!

[akinomyoga]

Oh man I didn't know this -- have you seen it documented anywhere?

I think I remember that it is explained by a simple one sentence in the manual. But today I found in the manual a detailed description with examples. Maybe the description is added recently.

From Shell Parameter Expansion (Bash Reference Manual)

If parameter is ‘@’, the result is length positional parameters beginning at offset. A negative offset is taken relative to one greater than the greatest positional parameter, so an offset of -1 evaluates to the last positional parameter. It is an expansion error if length evaluates to a number less than zero.

The following examples illustrate substring expansion using positional parameters:

$ set -- 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
$ echo ${@:7}
7 8 9 0 a b c d e f g h
$ echo ${@:7:0}

$ echo ${@:7:2}
7 8
$ echo ${@:7:-2}
bash: -2: substring expression < 0
$ echo ${@: -7:2}
b c
$ echo ${@:0}
./bash 1 2 3 4 5 6 7 8 9 0 a b c d e f g h
$ echo ${@:0:2}
./bash 1
$ echo ${@: -7:0}

[andychu]

Thanks a lot! I merged and moved the test cases to var-op-slice (renamed from var-op-other).