Shell Learning--Regular expression

1. Explanation: A single string that describes or matches a series of strings that conform to a certain syntactic rule.

Action object: String

Many are used in document editors or other tools to retrieve and replace text content that conforms to patterns.

Common Grep,sed,awk

2.grep filtering, printing;-incvabc

-I ignores case,-n displays line numbers, and-c counts the number of rows that meet the requirements;-V prints rows that do not conform to the requirements,-an prints rows that match and the next n rows,-bn on n rows,-cn up and down n rows.

grep ' halt '-n-a2/home/jason/passwd prints the line that meets the requirements and the following two lines, plus the line number display

grep ' bash '-c passwd prints rows that meet the required line number

Grep-nv ' nologin ' passwd prints lines without nologin and displays line numbers

grep ' [0-9] ' passwd prints all rows that contain numbers

Grep-v ' ^# ' inittab print all lines that do not start with #

Grep-v ' ^# '/home/jason/inittab |grep-v ' ^$ ' prints all lines that do not start with # and are not empty

Vim Greptest2.txt

123

Abc

55W

abc2345

#ljadj

grep ' ^[^a-za-z] ' greptest2.txt prints lines that do not start with a letter, [^] table negation, except for characters inside []

grep ' [^a-za-z] ' greptest2.txt contains characters other than letters

Shell Learning--Regular expression