SSH, The Secure Shell: The Definitive Guide, 2nd Edition

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.

[ Start a character set. See "Character Sets for Egrep and ZSH_FILEGLOB.”

$ 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 ...