Regex Syntax: Egrep Patterns

The escape character is a backslash (\). You can use it to escape metacharacters to use them in their plain character form.

In the following examples, literal E and F denote any expression, whether a pattern or a character:

( Start a capturing subexpression.

) End a capturing subexpression.

E|F: Disjunction, match either E or F (inclusive). E is preferred if both match.
E*: Act as Kleene star, match E zero or more times.
E+: Closure, match E one or more times.
E?: Option, match E optionally once.

. Match any character except for newline characters (\n, \f, \r) and the NULL byte.

E{ n }: Match E exactly n times.
E{ n ,} or E{ n ,0}: Match E n or more times.
E{, n } or E{0, n }: Match E at most n times.
E{ n , m }: Match E no less than n times and no more than m times.

$ Match the empty string at the end of the input or at the end of a line.

^ Match the empty string at the start of the input or at the beginning of a line.

Escaped Tokens for Regex Syntax Egrep

The following list describes the tokens:

\0 n .. n: The literal byte with octal value n .. n.
\0: The NULL byte.
\[1-9].. x: The literal byte with decimal value [1-9].. x.
\x n .. n or\0x n .. n: The literal byte with hexadecimal value n .. n.
\<: Match the empty string at the beginning of a word.
\>: Match the empty string at the end of a word.
\b: Match the empty string at a word boundary.
\B: Match the empty string provided it is not at a word boundary.
\w: Match a word-constituent character, equivalent to [a:zA:Z0:9-].
\W: Match a non-word-constituent character.
\a: Literal alarm character.
\e: Literal escape character.
\f: Literal line feed.
\n: Literal newline, equivalent to C’s \n so that it can be more than one character long.
\r: Literal carriage return.
\t: Literal tab.

All other escaped characters denote the literal character itself.