Run grep, searching for REGEXP in FILES in directory DIR.
The search is limited to file names matching shell pattern FILES.
FILES may use abbreviations defined in `grep-files-aliases', e.g.
entering `ch' is equivalent to `*.[ch]'.
With C-u prefix, you can edit the constructed shell command line
before it is executed.
With two C-u prefixes, directly edit and run `grep-command'.
Collect output in a buffer. While grep runs asynchronously, you
can use C-x ` (M-x next-error), or
Uses keymap `grep-mode-map', which is not currently defined.
M-x compile-goto-error in the grep output buffer,
to go to the lines where grep found matches.
This command shares argument histories with M-x rgrep and M-x grep.
(fn REGEXP &optional FILES DIR CONFIRM)