Find keywords in files (logs) under Linux

1 View the first n lines of the log:

cat 或者 tail 日志文件名 | head -n 数量
 
示例1 ：cat  api.log | head -n 200　　 # 查看log前200行
 
示例2： tail  api.log | head -n 10     # 查看log前10行

2 View the last n lines of the log:

cat   或者 tail 日志文件名 | tail -n 数量
 
示例： cat  api.log | tail -n 200　　 # 查看log后200 行
 
示例： tail  api.log | tail -n 15     # 查看log后15 行

3 Search the log according to the keyword and return all the lines where the keyword is located:

3.1 Method 1:

cat  或者 tail 日志文件名 | grep  "关键词"

示例1：cat  api.log | grep "前端入参" # 返回log日志中包含“前端入参”字样的所有行 
示例2：tail  api.log | grep "前端入参" # 返回log日志中包含“前端入参”字样的所有行

3.2 Method 2:

grep -i  "关键词" 日志文件名
 
示例1：grep -i  "21DYN60587" catalina.out # 返回log日志中包含 21DYN60587 的所有行

Common parameters:

parameter	illustrate
-f	Display the latest appended content of the file
-q	When there are multiple file parameters, do not output individual file names
-v	When there are multiple file parameters, always output the individual file names
-c [number of bytes]	Display the last n bytes of the file
-n [number of lines]	Display the content of the last n lines of the file

Common parameters:

parameter	illustrate
-n or –number	show line number
-b or --number-nonblank	Display line numbers, but do not number blank lines
-s or --squeeze-blank	When there are more than two consecutive blank lines, only one blank line will be displayed\