Find text in files recursively using grep

find_in_files_grep

grep -rnw '/path/to/somewhere/' -e "pattern"
-r or -R is recursive,
-n is line number, and
-w stands match the whole word.
-l (lower-case L) can be added to just give the file name of matching files.
Along with these, --exclude or --include parameter could be used for efficient searching. Something like below:
grep --include=\*.{c,h} -rnw '/path/to/somewhere/' -e "pattern"
This will only search through the files which have .c or .h extensions. Similarly a sample use of --exclude:

grep --exclude=*.o -rnw '/path/to/somewhere/' -e "pattern"
Above will exclude searching all the files ending with .o extension. Just like exclude file it's possible to exclude/include directories through --exclude-dir and --include-dir parameter; for example, the following shows how to integrate --exclude-dir:

grep --exclude-dir={dir1,dir2,*.dst} -rnw '/path/to/somewhere/' -e "pattern"