I have searched on the forum but can't find the answer, apologies if it is just that I am blind!
Ok, I have files with the length in the title such as :
"La Notte Etterna [ 5:43 ]"
"Just You & I [ 5:36 ]"
Specifically I want to know how to replace everything between the "[" and "]" using a wildcard. Also to replace the "[" and "]" for another folder.
Thanks in advance for any help
How should the final title looks like?
"Just You & I [ ]"
"Just You & I []"
"Just You & I "
"Just You & I"
Something else?
To be honest I'd like to know (if possible) how to achieve all of the above variations!
Thanks again for any help
Aktionstyp: Ersetzen mit regulären Ausdrücken
Feld: TITLE
Regulärer Ausdruck: [(.*)]
Treffer ersetzen durch:
This regular expression will match your [ xx:yy ]. If you replace it with nothing, you get the title without any length-information.
JFYI: You will get a space at the end of the title!
It's up to you to change this regular expression for your other variations. 
Thanks for the reply but is there any chance of an explanation then I don't have to keep pestering people for replies! It works great, but I can't understand why it works!
[(.*)] If you have time I would appreciate a quick rundown of how you arrived at this solution. For example what does the "" character do? How do I eliminate everything between 2 characters such as "[" and "]" and leave the "[" and "]" behind, or replace what is between those characters with something else?
I appreciate your help and totally understand if you don't get a chance to explain it, or indeed if the explanation is too involved for a mere mortal like me to grasp!
Once again, thanks a lot
[ and ] are special characters just like . is for example. In order to treat those brackets as brackets and not as special character you have to escape them with a backslash. This is described in the help file: https://docs.mp3tag.de/actions/replace-regexp. The paranthesis denotes that the characters inside it should be seen as a group and is only needed when you need to access that group later by using $1, or $2 or whatever (depending how many groups you have). A dot stands for a character and the asterisk means that it can occur any number of times, so .* matches an unlimited number of characters. The final string [(.)] or [.] which would be OK for you too says that the RegExp engine should look for a square bracket followed by an unlimited number of characters followed by another closing square bracket. All this should be replaced with nothing -> should be deleted.
@Sebastian: Thanks!
@percepto: Just Google for RegExp. Maybe this http://www.greenend.org.uk/rjk/2002/06/regexp.html or this http://www.regular-expressions.info/ can be a starting point.