Shell Programming and Scripting

I am new to UNIX Shell. I want to list the files names in the current directory that are not start with 'AB' and have at least two characters. For example, say I have those files in the current directory: AB, AC, AD, AE, B, C. After executing the command, AC, AD, AE will be listed on the screen.
My strategy is to get those files that their names have more than one character and use pipeline to redirect to another echo for filtering those files names that do not start with AB. I have tried the following command:

Code:

echo [!?] | echo [!A][!B]*

It seems it works fine, however, I am not sure wether I am correct. Is there any other way to do this? BTW, I am getting confused about the the differences between

Code:

echo [!A][!B]* | echo [!?]

and

Code:

echo [!?] |echo [!A][!B]*

I know that the first one is pass the results that do not start with AB to the second echo to filter files names longer than one character, the second one does the reverse order, however, they gave me different answers. I thought they should perform exactly the same. Could anybody explain the differences? and why I get different answers? I appreciate that.

echo cannot accept stdin, so you cannot pipe output of another command into it. But how about just:

Code:

ls [!A][!B]*

I want to retrieve files whose names have at least two characters but do not start with 'AB'. The command : ls [!A][!B]* just list files that do not start with 'AB', thus, file AC will not appear in the result, however, it should be.

Ow yes, that will also not list files that start with "A" . This should work better:

Code:

ls [!A]?* A[!B]*

It seems it works perfectly fine. Can I understand the code in this way that [!A]?* filters those files not start with A, however, have at least two characters and A[!B]* catches those files start with A, however, not AB? Does ls command combine the results in terms of two criteria together? Thanks!

Your understanding is correct for the first part, but

Code:

[!A]?* A[!B]*

Are two patterns that produce one field list, so it is not the command that glues them together. These fields are input to the command ls. They would need to be mutually exclusive.
You can see what is looks like if you first type:

Code:

set -x

and issue the command. Later you can switch it off with set +x


If for either pattern there is at least one file present, then you could for example also use:

Code:

printf "%s\n" [!A]?* [A[!B]*

You could also use bash extend globbing:

Code:

bash$ shopt -s extglob
bash$ ls
AB  AC  AD  AE  B  C
bash$ ls !(AB*|?)
AC  AD  AE