Add a new element to an array without specifying t

问题:

Is there a way to do something like PHPs $array[] = \'foo\'; in bash vs doing:

array[0] = \'foo\'
array[1] = \'bar\'

回答1:

Yes there is:

ARRAY=()
ARRAY+=(\'foo\')
ARRAY+=(\'bar\')

Bash Reference Manual:

In the context where an assignment statement is assigning a value to a shell variable or array index (see Arrays), the ‘+=’ operator can be used to append to or add to the variable\'s previous value.

回答2:

As Dumb Guy points out, it\'s important to note whether the array starts at zero and is sequential. Since you can make assignments to and unset non-contiguous indices ${#array[@]} is not always the next item at the end of the array.

$ array=(a b c d e f g h)
$ array[42]=\"i\"
$ unset array[2]
$ unset array[3]
$ declare -p array     # dump the array so we can see what it contains
declare -a array=\'([0]=\"a\" [1]=\"b\" [4]=\"e\" [5]=\"f\" [6]=\"g\" [7]=\"h\" [42]=\"i\")\'
$ echo ${#array[@]}
7
$ echo ${array[${#array[@]}]}
h

Here\'s how to get the last index:

$ end=(${!array[@]})   # put all the indices in an array
$ end=${end[@]: -1}    # get the last one
$ echo $end
42

That illustrates how to get the last element of an array. You\'ll often see this:

$ echo ${array[${#array[@]} - 1]}
g

As you can see, because we\'re dealing with a sparse array, this isn\'t the last element. This works on both sparse and contiguous arrays, though:

$ echo ${array[@]: -1}
i

回答3:

$ declare -a arr
$ arr=(\"a\")
$ arr=(\"${arr[@]}\" \"new\")
$ echo ${arr[@]}
a new
$ arr=(\"${arr[@]}\" \"newest\")
$ echo ${arr[@]}
a new newest

回答4:

If your array is always sequential and starts at 0, then you can do this:

array[${#array[@]}]=\'foo\'

# gets the length of the array
${#array_name[@]}

If you inadvertently use spaces between the equal sign:

array[${#array[@]}] = \'foo\'

Then you will receive an error similar to:

array_name[3]: command not found

回答5:

With an indexed array, you can to something like this:

declare -a a=()
a+=(\'foo\' \'bar\')