Bash Array – Get Index of Last Element Without Loop

As of bash 4.2, you can just use a negative index ${myarray[-1]} to get the last element. You can do the same thing for the second-last, and so on; in Bash:

If the subscript used to reference an element of an indexed array evaluates to a number less than zero, it is interpreted as relative to one greater than the maximum index of the array, so negative indices count back from the end of the array, and an index of -1 refers to the last element.

The same also works for assignment. When it says "expression" it really means an expression; you can write in any arithmetic expression there to compute the index, including one that computes using the length of the array ${#myarray[@]} explicitly like ${myarray[${#myarray[@]} - 1]} for earlier versions.

I think you're asking two different things there.

Is there a way to make bash print this info without the loop?

Yes, but they are not as good as just using the loop.

Is there a cleaner way to get/print only the key=value portion of the output?

Yes, the for loop. It has the advantages that it doesn't require external programs, is straightforward, and makes it rather easy to control the exact output format without surprises.

Any solution that tries to handle the output of declare -p (typeset -p) has to deal with a) the possibility of the variables themselves containing parenthesis or brackets, b) the quoting that declare -p has to add to make it's output valid input for the shell.

For example, your expansion b="${a##*(}" eats some of the values, if any key/value contains an opening parenthesis. This is because you used ##, which removes the longest prefix. Same for c="${b%% )*}". Though you could of course match the boilerplate printed by declare more exactly, you'd still have a hard time if you didn't want all the quoting it does.

This doesn't look very nice unless you need it.

$ declare -A array=([abc]="'foobar'" [def]='"foo bar"')
$ declare -p array
declare -A array='([def]="\"foo bar\"" [abc]="'\''foobar'\''" )'

With the for loop, it's easier to choose the output format as you like:

# without quoting
$ for x in "${!array[@]}"; do printf "[%s]=%s\n" "$x" "${array[$x]}" ; done
[def]="foo bar"
[abc]='foobar'

# with quoting
$ for x in "${!array[@]}"; do printf "[%q]=%q\n" "$x" "${array[$x]}" ; done
[def]=\"foo\ bar\"
[abc]=\'foobar\'

From there, it's also simple to change the output format otherwise (remove the brackets around the key, put all key/value pairs on a single line...). If you need quoting for something other than the shell itself, you'll still need to do it by yourself, but at least you have the raw data to work on. (If you have newlines in the keys or values, you are probably going to need some quoting.)

With a current Bash (4.4, I think), you could also use printf "[%s]=%s" "${x@Q}" "${array[$x]@Q}" instead of printf "%q=%q". It produces a somewhat nicer quoted format, but is of course a bit more work to remember to write. _{(And it quotes the corner case of @ as array key, which %q doesn't quote.)}

If the for loop seems too weary to write, save it a function somewhere (without quoting here):

printarr() { declare -n __p="$1"; for k in "${!__p[@]}"; do printf "%s=%s\n" "$k" "${__p[$k]}" ; done ;  }  

And then just use that:

$ declare -A a=([a]=123 [b]="foo bar" [c]="(blah)")
$ printarr a
a=123
b=foo bar
c=(blah)

Works with indexed arrays, too:

$ b=(abba acdc)
$ printarr b
0=abba
1=acdc