Example Analysis of regular expressions in CentOS

This article mainly introduces the example analysis of regular expressions in CentOS, which has a certain reference value, and interested friends can refer to it. I hope you will gain a lot after reading this article.

The tools that support linux regular expressions are: grep: implement search, sed,awk: are streaming editors that can find and replace, and output the replaced text to the screen.

Grep tool

Grep [- cinvABC] 'word'

-c: print the number of lines that meet the requirements

-I: ignore case

-n: output lines and line numbers that meet the requirements.

-v: print lines that do not meet the requirements

-A: followed by a number (with or without spaces),-A2 means to print the lines that meet the requirements and the following two lines

-B: followed by a number,-B3 prints the lines that meet the requirements and the three lines above.

-C: followed by a number,-C24 prints lines that meet the requirements and four lines up and down

# grep-c 'a'1.txt

# grep-A3 'a'1.txt

# grep-n 'b' 1.txt filters rows with keywords to display line numbers.

# grep-nv 'ab' 1.txt lines and line numbers that do not meet the requirements

# grep [0-9] 1.txt filters out all rows that contain numbers

# grep-v [0-9] 1.txt filters out rows that do not contain numbers

# grep-v'^ # '1.txt filters out all lines that begin with #

# grep-v'^ # '1.txt | grep-v' ^ $'filter out all blank lines and lines starting with # ($means ending, blank lines can be represented by ^ $)

Sed tool

Sed-n 'a'p filename an is a number that indicates the number of lines, and-n represents the lines we want to print. Unimportant content is not displayed.

# sed-n '2roomp 1.txt displays the second line

# sed-n '1re10 1.txt displays 1-10 lines of content

# sed-n'1 recording 1.txt displays all lines

# sed-n'/ aa/'p 1.txt prints lines containing aa

Add-e to achieve a variety of behaviors

# sed-e '1roomp-e' / aabb/'p-n 1.txt displays the first line and the line containing aabb

When querying, exclude certain rows

When sed'1' d 1.txt displays everything, the first line is excluded.

Sed '1jin3 1.txt excludes lines 1 to 3

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