ripgrep is a command line search tool that combines the usability of The Silver Searcher (an ack clone) with the raw speed of GNU grep. Why should I use ripgrep?

It can replace both The Silver Searcher and GNU grep because it is faster than both. (N.B. It is not, strictly speaking, a "drop-in" replacement for both, but the feature sets are far more similar than different.) Like The Silver Searcher, ripgrep defaults to recursive directory search and won't search files ignored by your .gitignore files. It also ignores hidden and binary files by default. ripgrep also implements full support for .gitignore, where as there are many bugs related to that functionality in The Silver Searcher. ripgrep can search specific types of files. For example, rg -tpy foo limits your search to Python files and rg -Tjs foo excludes Javascript files from your search. ripgrep can be taught about new file types with custom matching rules. ripgrep supports many features found in grep, such as showing the context of search results, searching multiple patterns, highlighting matches with color and full Unicode support. Unlike GNU grep, ripgrep stays fast while supporting Unicode (which is always on).

In other words, use ripgrep if you like speed, sane defaults, fewer bugs and Unicode.