Bash arrays and negative subscripts, yes or no?

问题

The GNU bash manual tells me

An indexed array is created automatically if any variable is assigned to using the syntax

name[subscript]=value

The subscript is treated as an arithmetic expression that must evaluate to a number. If subscript evaluates to a number less than zero, it is used as an offset from one greater than the array’s maximum index (so a subcript of -1 refers to the last element of the array).

So I figure I will give it a try and get the following result:

$ muh=(1 4 'a' 'bleh' 2)
$ echo $muh
1
$ echo ${muh[*]}
1 4 a bleh 2    # so far so good so now I'll try a negative ...
$ echo ${muh[-1]}
-bash: muh: bad array subscript  # didn't go as planned!

Did I do something wrong, or is the website wrong, or is gnu bash that different from the bash I am running under CentOS? Thanks!

回答1:

If you just want the last element

$ echo ${muh[*]: -1}
2

If you want next to last element

$ echo ${muh[*]: -2:1}
bleh

回答2:

According to Greg Wooledge's wiki, (which links to the bash changelog) the negative index syntax was added to bash in version 4.2 alpha.

回答3:

If you do man bash the section on arrays does not list this behavior. It might be something new (gnu?) in bash.

Fails for me in CentOS 6.3 (bash 4.1.2)

回答4:

The negative subscript works perfectly fine for me on my computer with Ubuntu 14.04 / GNU bash version 4.3.11(1) however it returns:

line 46: [-1]: bad array subscript

When I try to run the same script on 4.2.46(1). I

来源：https://stackoverflow.com/questions/16109652/bash-arrays-and-negative-subscripts-yes-or-no