Shell learns the third day--grep, SED, awk

Grep

In the past, we used grep to find lines in a file that contained certain strings, such as finding a string in a header file that fits a pattern (pattern), such as finding all strings that conform to the [email protected] pattern (that is, the email address). Requires an X character to be a letter, a number, an underscore, a decimal point.

Character class qualifier (Character Class): As in the example above X and Y, they represent a character in the pattern, but the range of values is any of a class of characters.

Quantity Qualifier (quantifier): Each part of a mailbox address can have one or more x characters.

Positional qualifiers (Achor): Describes the positional relationships between individual character classes and ordinary characters, such as mail addresses in three parts, separated by ordinary characters @ and.

Each section can be described with a character class and a quantifier, and in order to represent a positional relationship, a positional qualifier is required. (with three concepts, every time you write a regular expression, you don't get confused)

Exe

192.168.1.11234.234.04.5678123.4234.045.678abcde

The command executed is:

[12] [0-9] {0,2}\. [12] [0-9] {0,2}\. [12] [0-9] {0,2} ' exe

The result of the execution is:

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We know that C variables and shell scripting variables are defined and used differently, with different expression capabilities, and C variables have various types, and shell script variables are strings.

Character class

Character	Meaning
.	Match any one character
[]	Match any one of the characters in parentheses
-	Denotes a range of characters within [] parentheses
^	At the beginning of [], matching any character outside of the characters in parentheses

Specific Use examples

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Quantity qualifier

Character	Meaning	Example
？	The unit immediately preceding it matches 0 or one time	localhost bash]$ echo "Hello" | Grep-e--color ' hell? ' Hello
+	The unit immediately preceding it should match one or more times	[Email protected] bash]$ echo "Helloooo" | Grep-e--color ' hello+ ' Helloooo
*	The unit immediately preceding it should match 0 or more times	[Email protected] bash]$ echo "Helloooo" | Grep-e--color ' hello* ' Helloooo [Email protected] bash]$ echo "Helloooo" | Grep-e--color ' helo* ' Helloooo

Position Qualifier

Character	Meaning
^	Match the position of the beginning
$	Match the position at the end of the line
\<	Match the position at the beginning of the word
\>	Match the position of the end of the word
\b	Match the position of the beginning or end of a word
\b	Match the beginning and end of a word

Demo results

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Example:

Use the following command to find the No and standard IP numbers

Grep-e ' [1,2][0-9]{0,2}\. [0-9] {1,3}\. [0-9] {1,3}\. [0-9] {1,3} ' exe

Looking for a standard mobile phone number

Grep-e ' 1[34578][0-9]{9} ' exe

Search for No and standard mailbox numbers

Grep-e ' [123456789][0-9]{4,11} @qq \.com$ '

Shell learns the third day--grep, SED, awk