4.1.2 grep with Multi-Word Strings
To find a pattern that is more than one word long, enclose the string
with single or double quotation marks:
$ grep "Louisa May" extensions
Louisa May Alcott x74236
grep can search for a string in groups of files.
When it finds a pattern that matches in more than one file, it prints the
name of the file, followed by a colon, then the line matching the pattern:
$ grep ar *
alaska:Alaska is the largest state in the United States.
wilde:book. Books are well written or badly written.