Can someone explain what's going on here. All of this is executed consecutively in the same shell.
$ array=(a b c)
$ echo "${array[*]}"
a b c
So far so good.
$ IFS=/ echo "${array[*]}"
a b c
That's ok, the expansion happened before the whole line got executed.
$ IFS=/ x="${array[*]}"
$ echo $x
a b c
Same here, the expansion happened first, and x got that value.
$ echo "${array[*]}"
a/b/c
But ${array[*]} got changed, and the change is permanent.
$ x="${array[*]}"
$ echo $x
a b c
Ok, this is normal, I think - the original, default IFS value was used to expand the array variable in this assignment.
$ echo "${array[*]}"
a/b/c
$
But this totally doesn't make sense to me. First, the default IFS is not used here. Second, the assignment x="${array[*]}" didn't affect the value of ${array[*]} the same way it did before, in IFS=/ x="${array[*]}".
When you use:
IFS=/ echo "${array[*]}"
Then IFS is set local to the echo command (although not used by echo)
When you use:
IFS=/ x="${array[*]}"
Then these are two separated variable assignment, one for IFS and one for x, so the IFS is now permanently changed to / as @jaypal mentioned.
When you use:
$ echo "${array[*]}"
Then - when quoted - the first character of IFS is used as an output field separator with expansion of the array
If it is unquoted, then it produces space separated fields:
$ echo ${array[*]}
Also, when you would use:
$ echo "${array[@]}"
Then each array element is expanded to a separate word, so the output field separator is not used so it becomes a single space..