Regular Expressions (2)

Egrep is to return a matching position instead of matching the string itself. Egrep returns the newline character is removed before the regular expression is checked.

If you match some characters that are the same as the metacharacters, but to make him meaningless, use "\" before the characters to represent the general meaning

^pepple-Represents a match to a $people that begins with a people line---represents a match that starts with a people line [^ ....] ----match in addition to the parentheses content

Metacharacters: "." can match any character set of characters shorthand to match 09-02-1 or 09.02.1 or 09/02/01

Regular expression "09[-. /]02[-./]01 "Where [-./] This symbol is not a meta-character, because inside a character group

Regular expression "09.02.01" this and the regular expression above a meaning, at this time the "." Represents a meta-character that can match any character

| The meaning of an expression or

For example: gr (e|a) y to match grey and Gray

The egrep command parameter line "-i" indicates a match that ignores the case

Egrep-i "^ (from|subject|date):"-I write in front of regular expressions

Egrep "/<" matches the beginning of the word, "/>" matches the end of the word: the word that is expected to match is in the other but this time

Egrep "/<cat/>" begins with a cat and ends with a cat word,

？ Represents an option

For example, match color and colour match, can be written as "(Colour)" This U is optional or optional

+ indicates that the immediate element appears one or more times, * indicates that the element immediately preceding it appears any number of times or does not appear

Example: Match 14

Available "[0-9]+"

Brackets and Reverse applications

Three uses of parentheses: 1) limit the range of multiple options 2) combine several characters into a single unit, subject to a question mark or a quantifier like an asterisk 3) for reverse referencing

Egrep the reverse reference

For example: We want to match an arbitrary word, and then we check to see if the following word is the same as it.

The regular expression:\< ([a-za-z]+) *+\1\> represents the beginning of the first matching word, ending with the last word that appears as the first word. "\1" "\2" "\3" to represent the first, second, and third set of bracketed text.

([A-z]) ([0-9]) \1\2 ". Brackets are in the order of opening parentheses "(" from left to right, so \1 ([a-z]) represents \2 ([0-9])

Regular Expressions (2)