This description can be used to search through a file by looking for text that matches the regular expression. A regular expression is made up of text and metacharacters . A metacharacter is just a character with a special meaning. For example, the regular expression ' my regular expression ' matches the text ' my regular expression ', and nothing else.
Regular expressions are usually case-sensitive.
You can use the egrep command to display all lines in a file which contain a regular expression. Matches any single character except newline. Matches zero or more occurences of the preceding thing. You can include ranges in a bracketed character list.