Advanced Usage of Linux Grep Command

Grep recursively: -R, -r, --recursive
grep -r "127" /etc

Use grep to search words only: -w, --word-regexp
Select only those lines containing matches that form whole words
grep -w "boo" file

-s, --no-messages
Suppress error messages about nonexistent or unreadable files.

Ignore binary files: -I
When we search, we may only want to search text files and ignore binary files for better performance. we can use: -I.
-I Process a binary file as if it did not contain matching data; this is equivalent to the --binary-files=without-match option.

Combine grep and find
grep "some_string" `find some_folder -name "*.some_extension"`
find . -name "*.php" -exec grep -H "some_string" {} \;

--include=GLOB
Search only files whose base name matches GLOB
--exclude=GLOB
Skip files whose base name matches GLOB (using wildcard matching). A file-name glob can use *, ?, and [...] as wildcards, and \ to quote a wildcard or backslash character literally.
--exclude-dir=DIR
grep -rsI --include=*.html --include=*.php --include=*.htm "pattern" /some/path/
grep -rsI --include=*.{html,php,htm} "pattern" /some/path/
grep -rsI --include=*.{py,pyc} hue /etc

Find jars that contain matched classes
Grep can be used to find the jar that contains the matched class fileL
grep -r com.cloudera.cmf.inspector.Inspector /usr/share/cmf/lib

Miscs
-c, --count
Suppress normal output; instead print a count of matching lines for each input file
-n, --line-number
-h, --no-filename
-H, --with-filename
-v, --invert-match
--color[=WHEN], --colour[=WHEN]
grep --color root /etc/passwd

Resources
Grep Manual