What is the linux command to view logs?

The Linux commands for viewing logs are: tail command and head command. Example: You can use "tail -n 10 test.log" to query all logs after the 10th line; you can use "head -n 10 test.log" to query the first 10 lines of logs in the log file.

Common commands to view logs

tail:

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

tail -100f test.log      实时监控100行日志
tail  -n  10  test.log   查询日志尾部最后10行的日志;
tail -n +10 test.log    查询10行之后的所有日志;

head:

is the opposite of tail, tail is to look after How many lines of logs; examples are as follows:

head -n 10  test.log   查询日志文件中的头10行日志;
head -n -10  test.log   查询日志文件除了最后10行的其他所有日志;

cat:

tac is viewed in reverse order, which means the word cat is written in reverse order; examples are as follows:

cat -n test.log |grep "debug"   查询关键字的日志

Application scenario one:

View by line number---filter out logs near keywords

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 log of the first 10 lines and the 10 lines of this keyword:

TAIL -N 92 indicates that the log of the query 92 lines

HEAD -N 20 means that you can check in the query results in the previous query The first 20 records

Application scenario two:

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 two dates above must be the logs printed in the log, otherwise they will be invalid;

                                       First grep '2014-12-17 16:17:20' test.log to determine whether there is this time point in the log

Application scenario three:

The log content is very large, and it is inconvenient to view it when printed on the screen.

(1) Use the more and less commands,

For example: cat -n test.log |grep "debug" |more This way Page printing is done, click the space bar to turn pages

(2) Use >xxx.txt to save it to a file. You can then pull down the file for analysis

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

Related recommendations: "Linux Video Tutorial"

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