Depending on the utility and its version, some versions support standard regular expressions and some support extended regular expressions. Although some of them may look like shell expansion characters they usually mean something else. Whenever you wish to match a special character literally it must be quoted.

Period is the only wildcard in regular expressions (RE). The period character in a regular expression can be viewed as a placeholder (match) for any single character. Some examples of period being used in regular expressions:

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Represents zero or more occurrences of regular expression directly preceeding the asterisk (<code>*</code>). By itself, it does not match anything - it is NOT a wildcard. It is used in conjunction with literal matches, a period or other special characters. Some examples of asterisk in regular expressions: