[file] How I can delete in VIM all text from current line to end of file?

I have very large files (more than 10Gb). I need only some lines from the top of the file. Is it possible (in vim) to delete the rest of the file (from current line to the end of file)?

:.,$d

This will delete all content from current line to end of the file. This is very useful when you're dealing with test vector generation or stripping.

Go to the first line from which you would like to delete, and press the keys dG

Just add another way , in normal mode , type ctrl+v then G, select the rest, then D, I don't think it is effective , you should do like @Ed Guiness, head -n 20 > filename in linux.