zathura-pdf-poppler | PDF support for zathura | Document Editor library

In your regex ([^.]*\).*, ( which actually is \( is the start of a capturing group and then [^.]* captures every character except a literal dot and * means zero or more, then \) is the mark of closing of group that we started, then .* captures whatever remains after capturing group1.

Similar will be the explanation for \(.*\)-.* regex, where \(.*\) will capture everything greedily in capturing group but will stop at last hyphen - and then will match hyphen and further .* will match remaining text.

To explain with an example, lets take youtube_dl-2018.12.03.

Here, \([^.]*\) will capture everything until dot, hence it will capture youtube_dl-2018 and then remaining .* will capture .12.03. Then it will be replaced by \1 which means youtube_dl-2018 will be passed to the next regex -e 's/\(.*\)-.*/\1/'.

Then in your second regex, \(.*\)-.*, \(.*\) will capture youtube_dl and put in group1 because after that there is a hyphen and .* will capture remaining text which is 2018. And as it is replaced by \1 hence final text will become youtube_dl.

Seeing your data, I believe, you can also simplify your command to this, as your first regex in sed command seems redundant. Try this following command and see if it outputs same result?