sed & awk, 2nd Edition

A Line-Up of Characters

We have seen two basic elements in an expression:

15. A value expressed as a literal or a variable.

16. An operator.

A regular expression is made up of these same elements. Any character, except the metacharacters in Table 3.1, is interpreted as a literal that matches only itself.

Table 3.1. Summary of Metacharacters

Special Characters	Usage
.	Matches any single character except newline. In awk, dot can match newline also.
*	Matches any number (including zero) of the single character (including a character specified by a regular expression) that immediately precedes it.
[...]	Matches any one of the class of characters enclosed between the brackets. A circumflex (^) as first character inside brackets reverses the match to all characters except newline and those listed in the class. In awk, newline will also match. A hyphen (-) is used to indicate a range of characters. The close bracket (]) as the first character in class is a member of the class. All other metacharacters lose their meaning when specified as members of a class.
^	First character of regular expression, matches the beginning of the line. Matches the beginning of a string in awk, even if the string contains embedded newlines.
$	As last character of regular expression, matches the end of the line. Matches the end of a string in awk, even if the string contains embedded newlines.
\{n,m\}	Matches a range of occurrences of the single character (including a character specified by a regular expression) ...