Matching negative patterns with bash extglob

Question

Consider I have a set of seven files:

item1_data
item2_data_more
item3_data
item4_data
item5_data_more
other6_data
other7_data_more

and I want to match the three of them that begin with item but do not end with more. Given that this is an example scenario you have to accept that it is not sufficient to match with the positive matching pattern item*data? (or any trivial variant).

I'm using bash with extglob enabled. For simple cases the description in the man page is sufficient ("!(pattern‐list) Matches anything except one of the given patterns"). However, here I need to achieve a match on item but a negative match for data. I finally landed on one that works but what I do not understand is why it works but others fail.

shopt -s extglob                                                # Enable extended globbing
touch {item{1,3,4},other6}_data {item{2,5},other7}_data_more    # Example data set

ls !(*more)                                                     # Non-"item" files too
item1_data  item3_data  item4_data  other6_data

ls item*!(more)                                                 # All "item" files
item1_data  item2_data_more  item3_data  item4_data  item5_data_more

ls item!(*more)                                                 # Works as required
item1_data  item3_data  item4_data

Why does the second of these fail and the third succeed? I'm thinking that the wildcard should be valid in either position - but clearly isn't. Can someone enlighten me, please.

Answer 1

I'd say the second expression fails because item* matches the entire filename for each of these files, and the empty string at the end trivially matches !(more).

Answer 2

The answer I needed is found in one of the other answers to the question In Bash, how can I rm files against a wildcard while supplying more than one exception referenced through a comment to my question.

The relevant phrase for me is this,

The key to note is that !(…) already acts like *, in that it itself matches anything that isn't one of the things inside.

I wasn't thinking of it as being equivalent to *, and that was the blocker to my understanding.