Linux Regular expressions

Character

Range of characters in a single character: [] [A-z]

Inverse character ^: [^ 0-9] not a number

Any character: '. ‘

Kinsoku characters: ^ $, ^root//note differs from [^], empty line represents ^$

Metacharacters and repeat settings:

character Combinations :

The representation of any string:. *

. Represents any one character, * represents more than one character, and the regular expression is the maximum range, which needs to be added to a smaller range according to the desired result.

Logical Representation :

| Logical OR

grep ' bin/\ (false\|true\) ' passwd

Example:

Match 2-3-bit numbers in the passwd file

This contains the number [0-9], repeat {,}, delimiter/b/b

Case 2:

Match 15-bit or 18-bit ID number (supported with X)

Because the first card number can not be 0, the last one with X, in the middle there are 13-16 duplicates, ^$ represents the first and the end

grep ' ^[1-9]\ ([0-9]\{13\}|[ 0-9]\{16\}\) [0-9xx]$ ' File

Case 3:

Match password (consisting of letters, numbers, underscores)

grep ' ^\w\+$ ' file

Summary chart:

Linux Regular expressions