Bad substitution error in zsh shell

arrayzsh

Hi in my previous question I got clarity on how to use associative arrays in zsh shell.

But whenever I trigger the following command in my script

for KEY in ${!array[@]} to iterate amongst the keys in my array

I get a bad substitution error.

even echo ${!array[@]} gives the same.

NB: array is the name of my associative array

Best Answer

zsh has different parameter substitution than Bash, which is documented in man zshexpn. It supports a variety of modifiers to expansion behaviour, which are put in parentheses before the variable name: ${(X)name}. The modifier to include array keys (including for associative arrays) is k: ${(k)array} expands to the list of keys in the array, except that if a key is the empty string, it is omitted. Use double quotes and the @ modifier to retain the empty key.

for x in "${(@k)array}" ; ...

will loop over the keys of the array array.

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Bash – command substitution handling in fish vs. other shells (sh, bash, zsh)

Ok, I think I have a clue what is going on.

The behaviour you are observing in zsh and bash when executing echo $(mc) is caused by mc.

When you run mc normally, it doesn't react when Ctrl+c is pressed, since it ignores SIGINT. The way to end mc is by pressing F10 and Enter.

When you run echo $(mc) the input goes to the mc process, so it is no wonder that when you press Ctrl+c nothing will happen, because mc ignores SIGINT. But when you run echo $(mc) and press F10 and Enter it will react. (When I then press F10 and Enter again it actually quits; it should quit at the first try but I have no idea why it does not.)

From this fact I deduce that Midnight Commander is running normally, but the output from it is put into the shell buffer, so it can later be used by echo. Something we should consider normal.

Also you think that bash and zsh are hanging, but I would say that they are not hanging but waiting for the echo command to return. But echo can only return when mc returns, which it only does when F10 and Enter are pressed. With this we can also explain what happens when you press Ctrl+z. By pressing the combination mc goes to sleep like it would if you had run mc normally and echo is still waiting for the sleeping mc.

So everything is normal behavior. Except for what fish does. fish seems to start commands run with echo ($command) in the background. It kind of makes sense, since such a command normally does not need any input. For the why and how I have no answer. But you can see that it runs in the background when you enter

echo (mc)
jobs

Bash Array – Resolving ‘typeset -A’ Error in Bash Script

That is the error generated by Bash 3 for typeset -A. Associative arrays were added in Bash 4, and are not in Bash 3.2 and earlier.

It seems that your script is being run with a different version of Bash than you are using as your shell. If you're on the same machine in both cases, you have multiple versions installed and can probably select one with a different path. If you're on a different machine running the script, you may be able to install a newer version, but otherwise you're out of luck for direct support in Bash.

zsh supports associative arrays since much older versions, so if you have that available you can likely port your script without too much work. If you're unable to do that, you can fake it with regular arrays and grep, or using ${!prefix@} and a set of ordinary variables, which is available in older Bash versions. ${!prefix@} expands to the names of all variables whose names start with prefix, which you can use in combination with several variables prefix_key1, prefix_another to get most of the behaviours of associative arrays.

Best Answer

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