Hi..
im a newbie in shell scripting, and also new in this forum..
i understand the command below is just reading from /etc/passwd
and getting whatever in field 1 and 3 (which are username and userID)

after the cut the format will be
username:uid
my guess,its making the array with the index in respect to its userID

but i dont understand the expression
{i#*:}]=${i%: *}
could somebody please explain how to read those...
and what those will evaluate to...
and how to work with things like those(i dont think those're regex-i have no clue)..

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for i in $(cut -f 1,3 -d: /etc/passwd) ; do array[${i#*:}]=${i%: *}done

This lets you see what is going on. is parameter substitution- returns the value just before the colon - a number that is the user id.
returns the username, so:
arr[number] = name

was changed from which doesn't work, by the way.
Try man (or info) for bash or ksh. This is called parameter substitution using a POSIX shell. It finds substrings.

bash's parameter substitution is a good feature to have, but it has ugly syntax. for what you want to do, you can use awk