Elisp programming 11: Regular Expression 1

Interactive Writing of Regular Expressions

For example, the buffer contains a string.

ABCD 3

Run the following command:

M-X: Re-Builder

A small buffer is displayed. Enter the regular expression D in double quotation marks. The buffer on the string is immediately highlighted with the D character. If the input is 3, the buffer is highlighted with three characters.

Special characters

Reference: http://www.gnu.org/software/emacs/manual/html_node/elisp/Regexp-Special.html#Regexp-Special

'.' Represents any character (except the line break), so "a. c" can match ABC in ABCD 3.

'*' Indicates that the previous character (string) can be repeated> = 0

For example, "E *" can also match ABCD 3 in re-builder, which may lead to confusion and is generally not used in this way.

In addition, if multiple characters are followed by *, as long as one character can be matched, this is a thing that does not know where it is used.

We recommend that you try not to use this.

If * is used at the beginning, it can only represent normal characters. The same situation applies to + and ?, In a word, special characters can only be used as common characters if they are not possible.

'+' Indicates that the previous character (string) must appear at least once.

For example, "BC + D" matches the above string ABCD 3

'? 'Indicates that the previous character (string) appears once or 0 times

'^' Matches the start of a string

'&' Matches the end of a string

[...] Can contain several characters, as long as it matches one of them.

For example, the string ABCD 3 AB

Use the regular expression "[BC]" to match three values: B c and the last B.

[^...] Indicates that it cannot contain any character in [].

\ Indicates that the special character following it is only a common character.

Note: To match the \ character in a string, four \ characters are required, for example, ABCD 3 AB \ EF.

Regular Expression :"\\\\"

First, because the \ in the double quotation marks is not displayed in the elisp string writing method, to display it, it must be two \

Then, in the regular expression syntax, \ is a special character, \ can represent \,

Therefore, "\\\\" is a logical regular expression "\\", so it matches the character \

'*? ''+? ''?? 'And' * '+ ''? 'Similar functions, only non-Greedy matching, only matching the most appropriate one.