What are the linux command application scenarios for viewing logs?

Editor to share with you to view the log of the linux command application scenarios, I believe that most people do not know much, so share this article for your reference, I hope you will learn a lot after reading this article, let's go to know it!

The linux commands for viewing logs are: tail command, head command. For example, you can use "tail-n + 10 test.log" to query all logs after 10 lines; you can use "head-n 10 test.log" to query the first 10 lines of logs in the log file.

Common commands for viewing logs

Tail:

-n is the display line number; equivalent to the nl command; examples are as follows:

Tail-100f test.log real-time monitor 100 lines of logs tail-n 10 test.log query the last 10 lines of the log; tail-n + 10 test.log query all logs after 10 lines

Head:

Contrary to tail, tail refers to the number of lines of log after reading. Examples are as follows:

Head-n 10 test.log queries the first 10 lines of logs in the log file; head-n-10 test.log queries all logs in the log file except the last 10 lines

Cat:

Tac is viewed in reverse order, which is the reverse of cat words. Examples are as follows:

Cat-n test.log | grep "debug" query the log of the keyword

Application scenario 1:

View by line number-filter out the log near the keyword

1) cat-n test.log | grep "debug" to get the line number of the key log

2) cat-n test.log | tail-n + 92 | head-n 20 Select the middle line where the keyword is located. Then check the log of the first 10 lines and the last 10 lines of this keyword:

Tail-n + 92 represents the log after 92 lines of the query

Head-n 20 means to check the first 20 records in the previous query results.

Application scenario 2:

Query log based on date

Sed-n'/ 2014-12-17 16-14-17 17-17 17-17 17-17-17 17-12-16-17 17-17-17 17-12-17 16-17-17 17-12-17 16-17-17-17-17-14-12-16-16-17-17-17-17-12-17-16-16-17-14-12-17 16-16-17 17-12-17 16-16-17 17-12-17 16-16-17 17-12-17 16-16-17 17-12-17 16-17 17-12-17 16-16-17 17-12-17 16-16-17 17-12-17 16-16-17 17-12-17 16-16-17 17-12-17 16-16-17 17-12-17 16-17 17-12-17

Special note: the above two dates must be the log printed in the log, otherwise it will be invalid

First grep '2014-12-17 16-16-14-17-17-17-17-17-17-16-17-17-17-17-16-17-17-17-16-17-17-17-16-17-12-16 to determine whether there is this time point in the log

Application scenario 3:

The content of the log is so much that it is not easy to view it when printed on the screen.

(1) use the more and less commands

For example: cat-n test.log | grep "debug" | more is printed in pages. Turn the page by clicking the spacebar.

(2) use > xxx.txt to save it to a file, and then you can pull down the file for analysis.

For example: cat-n test.log | grep "debug" > debug.txt

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