1. Command function
cat Merge files or view file contents.
2. Grammar format
cat option file
Parameter Description
| parameter |
Parameter Description |
| -n |
Print the text, showing each line number and blank lines as well |
| -b |
Similar to the usage of -n, the difference is that -b does not display the line number of blank lines, and ignores blank line numbers |
| -s |
When encountering more than 2 consecutive blank lines, reset to one line |
| -E |
Add a $ sign at the end of each line |
| -e |
Equivalent to -vE |
The cat command is divided into three categories:
- Merge multiple files and output to standard
- Append file to another file
- Usage syntax for creating files and writing file contents: cat > filename <<EOF
3. Example of use
Example 1 Display file content
[root@localhost home]# cat passwd_test
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
saslauth:x:499:76:Saslauthd user:/var/empty/saslauth:/sbin/nologin
postfix:x:89:89::/var/spool/postfix:/sbin/nologi
cxf:x:500:500::/home/cxf:/bin/bash
Example 2 Display line number cat -n
[root@localhost home]# cat -n passwd_test
1 root:x:0:0:root:/root:/bin/bash
2 bin:x:1:1:bin:/bin:/sbin/nologin
3
4 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
5
6
7
8 vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
9 saslauth:x:499:76:Saslauthd user:/var/empty/saslauth:/sbin/nologin
10
11 postfix:x:89:89::/var/spool/postfix:/sbin/nologi
12 cxf:x:500:500::/home/cxf:/bin/bash
Example 3 Blank lines do not display line numbers
[root@localhost home]# cat -b passwd_test
1 root:x:0:0:root:/root:/bin/bash
2 bin:x:1:1:bin:/bin:/sbin/nologin
3 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
4 vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
5 saslauth:x:499:76:Saslauthd user:/var/empty/saslauth:/sbin/nologin
6 postfix:x:89:89::/var/spool/postfix:/sbin/nologi
7 cxf:x:500:500::/home/cxf:/bin/bash
Example 4 Multiple consecutive blank lines, reset to one blank line
[root@localhost home]# cat -sn passwd_test
1 root:x:0:0:root:/root:/bin/bash
2 bin:x:1:1:bin:/bin:/sbin/nologin
3
4 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
5
6 vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
7 saslauth:x:499:76:Saslauthd user:/var/empty/saslauth:/sbin/nologin
8
9 postfix:x:89:89::/var/spool/postfix:/sbin/nologi
10 cxf:x:500:500::/home/cxf:/bin/bash
Example 5 cat merge multiple files
[root@localhost test]# cat 1.txt
123 123
123 123
[root@localhost test]# cat 2.txt
234 234
234 234
[root@localhost test]# cat 1.txt 2.txt
123 123
123 123
234 234
234 234
Example 6 cat append (create file when appending file does not exist)
[root@localhost test]# cat 1.txt 2.txt > 3.txt
[root@localhost test]# cat 3.txt
123 123
123 123
234 234
234 234
Example 7 cat does not overwrite append
[root@localhost test]# cat 1.txt 2.txt >> 3.txt
[root@localhost test]# cat 3.txt
123 123
123 123
234 234
234 234
123 123
123 123
234 234
234 234
Example 8 cat write to file
[root@localhost test]# cat > test.txt << EOF
> HELLO WORLD
> WELCOME TO LINUX
> EOF
[root@localhost test]# cat test.txt
HELLO WORLD
WELCOME TO LINUX
Example 9 cat appends files without overwriting
[root@localhost test]# cat >> test.txt << EOF
> OK OK OK
> EOF
[root@localhost test]# cat test.txt
HELLO WORLD
WELCOME TO LINUX
OK OK OK