Regular Expression (basic)

1. The meta character of the regular expression: \ escape character. match a single character * match the first character (0) ^ match the followed regular expression, and match the regular expression at the beginning of the line $, the position at the end of the row [] matches the expression of any character \ {n, m \} in square brackets. The number of times that a single character matches before it \ {n \} indicates
1, Regular ExpressionMeta character of the expression:
\ Escape Character
. Match a single character
* Match the first character (> = 0)
^ Match followed Regular ExpressionAt the beginning of the row
$ Match the regular expression at the end of the row
[] Matching any character in square brackets
\ {N, m \} region expression, matching the number of times a single character is reproduced before it
\ {N \} indicates n times,
\ {N ,\} indicates at least n occurrences
\ {, M \} indicates a maximum of m occurrences
\ (\) Stores the mode between parentheses in a special reserved space, up to 9
Then, call in the same mode, such as \ (ac \). * \ 1.
Will find the achhehekehac string
\ N is usually used in combination with \ (\), 1 + Match one or more instances of the previous Regular Expression
? Matches zero or one instance of the previous regular expression.
| Match | regular expression before or after
() Regular expression group matching square brackets
2. POSIX character set:
[: LnUm:] numeric characters
[: Alpha:] letter
[: Blank:] space and tab)
[: Cn TrL:] control characters
[: Di Git:] Numeric characters
[: Graph:] non-space characters
[: Lower:] lowercase letter
[: Print:] printable characters
[: Pu NcT:] punctuation characters
[: Space:] blank characters
[: Upper:] uppercase characters
[: Xdigit:] hexadecimal number
3. Integration Grep CommandUsed to find the content required for selection according to the Regular Expression
Grep parameters:
-I is case insensitive.
-V returns an inverse value in the specified search result.
-N: displays the row number of the matched row in the file.
-An matches the first n rows of a row
-Bn matches the last n rows of a row
-Cn matches n rows before and after each row
-- ColOr highlighted
-E = EgrepExpand grep. Example: 1. See the specified string. You can see that the row of the specified aaa is selected, highlight 2. Select a line starting with a space. You can see that the line starting with a space is selected, that is, the fourth line. However, the color of the space is not displayed. You need to select a reversed line to see the color. 3. Select any string in the middle starting with aA, followed by the line ending with aA. 4. Select the line starting with a space and the aA line appears twice, there are other strings between the two aA. 5. You must select aA and aA will appear at a later position to show aA for multiple times and end with aA, for example: 6. Select the line 7 that starts with aAxy and ends with xyaA and display the-compliant character. The line appears three to six times again, as shown in the figure above, which is a basic regular expression, the following blog will introduce the extended regular expressions.