Linux cat command

cat command is used to view the content of a file without opening it in any text editor. Another major use of the cat command is to concatenate multiple files into a single file.

parameter

parameter	meaning
-n	Show line numbers (empty lines are also numbered)
-s	Merge multiple empty lines into one line
-b	Show line numbers (empty lines are not numbered)
-e	Display $ at the end of each line
--help	show help
--version	show version information

grammar 

cat <option> <filename1 filename2 filename3>

example

View Files

cat 123.txt

 View all files in the current folder

cat *

View all files of the specified format in the current folder

cat *.txt

Display multiple files at once

cat t1.txt t2.txt

Copy output from one file to another

If the target file does not exist, it will first create it, otherwise append the contents to the target file.

 cat t1.txt > t2.txt

Append the output of one file to another

If the target file does not exist, it will first create it, otherwise it will overwrite the target file.

cat t1.txt >> t2.txt

Append the sequential output of multiple files to another file

cat t1.txt t2.txt >> t3.txt

content filtering

#在error.log文件中不包含org.apache.catalina.authenticator的行
cat -n  error.log |grep -v 'org.apache.catalina.authenticator'

#在error.log文件中包含org.apache.catalina.authenticator的行，并显示后面的5行信息
cat -n  error.log |grep 'org.apache.catalina.authenticator' -A 5

#在error.log文件中包含org.apache.catalina.authenticator的行，并显示前面的5行信息
cat -n  error.log |grep 'org.apache.catalina.authenticator' -B 5

#在error.log文件中包含org.apache.catalina.authenticator的行，并显示前、后的5行信息
cat -n  error.log |grep 'org.apache.catalina.authenticator' -C 5