Extended regularity of regular expressions

Extended regularity

Extended regularity means that the expression contains: +? | | {} and other symbols cannot be used directly in grep. You need to add\ extension |

If you don't want to add\ topology, you can use egrep or grep-E.

Extended regular: sed-r, and grep options, with +? | | r option is required when {} symbol is added, and\ topology is required if it is not added. |

Awk supports all functions of grep and sed by default.

The size of awk cannot be compared with numbers and letters, and this comparison cannot be made.

Extended regular? + | {}

? Extended regular representation:? There are 0 or 1 characters before it

A1? = > an or A1

The extended regular means that there are positive integers before the + characters.

| | extended regular representation: or |

{} indicates range

Some of the meanings of special symbols:

. Represents any one character

A b 0: the preceding character has 0 or more

Abc

Ab abccc

. It means greedy matching.

Egrep 'abc | 123' 1.txt

[] represents a character in square brackets

[a-zA-Z0-9] [abc] [a | @] [^]

^ indicates the beginning

$indicates the end

A {1,5} b {3}

() the characters in parentheses are regarded as a whole

(abc) {2} = "abcabc

(abc) +

Abc {2} = = > abcc

Awk-F'[#: |]'