Common commands for viewing logs in Linux

Commands to view logs: 1. tail command, for example "tail -n 10 test.log" to query all logs after 10 lines; 2. head command, for example "head -n 10 test.log" to query The first 10 lines of logs in the log file; 3. cat command; 4. sed command.

1.linux Common commands for viewing logs

tail:

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

tail -100f test.log Real-time monitoring of 100 lines of logs

tail -n 10 test .log Query the last 10 lines at the end of the log;

tail -n 10 test.log Query all the logs after the 10th line;

head:

It is the opposite of tail, tail is the number of log lines after looking at it; the example is as follows:

head -n 10 test.log Query the first 10 lines of logs in the log file;

head - n -10 test.log Query all logs except the last 10 lines of the log file;

cat:

tac is viewed in reverse order, and the word cat is written in reverse; example As follows:

cat -n test.log |grep "debug" Query the log of keywords

2. Application scenario 1: View by line number---Filter Get the logs near the keyword

1) cat -n test.log | grep "debug" 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 view the logs of the 10 lines before and 10 lines after the keyword:

tail -n 92 means querying the lines after line 92 Log

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

3. Application scenario 2: Query the log based on date

sed -n '/2014-12-17 16:17:20/,/2014-12-17 16:17:36/p' test.log

Special Note: The above two dates must be printed in the log, otherwise they will be invalid;

First grep '2014-12-17 16:17:20' test.log to determine whether the time exists in the log Click

4. Application scenario three: The log content is very large, and it is inconvenient to view it when printed on the screen

(1) Use more and less Command,

such as: cat -n test.log |grep "debug" |more This will print in pages, click the space bar to turn pages

(2) Use>xxx.txt 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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