how to manipulate array in shell script

Question

I want my script to define an empty array. array values should be added if predefined condition gets true. for this what i have done is

declare -a FILES
file_count=0
if [ "$file_ext" != "$SUPPORTED_FILE_TYPE" ] ; then
        echo "$file_ext is not supported for this task."
else
        $FILES[$file_count] = $filename
        file_count=$file_count+1
fi

when executing this script i am getting some error like this

linux-softwares/launchers/join_files.sh: 51: [0]: not found

Answer 1

When settings data in array does not recall with $:

declare -a FILES
file_count=0
if [ "$file_ext" != "$SUPPORTED_FILE_TYPE" ] ; then
        echo "$file_ext is not supported for this task."
else
        FILES[$file_count]=$filename
        file_count=$file_count+1
fi

FILES without $.

---

This works for me:

#!/bin/bash
declare -a FILES
file_count=0

file_ext='jpg'
SUPPORTED_FILE_TYPE='jpg'
filename='test.jpg'

if [ "$file_ext" != "$SUPPORTED_FILE_TYPE" ] ; then
        echo "$file_ext is not supported for this task."
else
        FILES[$file_count]=$filename
        file_count=$(($file_count+1))
fi

As you see, a little modification $(( )) for math operation, but the FILES assignements is the same...

---

As pointed out after lots of tests, Ubuntu default shell seems to be dash, which raised the error.