Notepad++ regex to remove text outside brackets?

Question

Regular Expressions

there is such a list
custom text [2015]\
custom text [2001] [text] [3 of 3]\
custom text [2007-2008] [text]\
custom text [1997-2001] [text] [4 of 4]\
arbitrary text [2001] [text]\
how to leave only what is in the first square brackets in each line, taking into account that in principle there can be only one of them or after them there can be one or two more pairs of brackets.

Answer 1

Regular expressions without newlines, replace
^[^\[]*\[([^\]]*).*$
with
$1