The cat (short for “concatenate“) command is one of the most frequently used command in Linux/Unix like operating systems. cat command allows us to create single or multiple files, view contain of file, concatenate files and redirect output in terminal or files. In this article, we are going to find out handy use of cat commands with their examples in Linux.
cat [OPTION] [FILE]...
1. Display Contains of File
In the below example, it will show contains of /etc/passwd file.
# cat /etc/passwd root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/sbin/nologin narad:x:500:500::/home/narad:/bin/bash
2. View Contains of Multiple Files in terminal
In below example, it will display contains of test and test1 file in terminal.
# cat test test1 Hello everybody Hi world,
3. Create a File with Cat Command
We will create a file called test2 file with below command.
# cat >test2
Awaits input from user, type desired text and press CTRL+D (hold down Ctrl Key and type ‘d‘) to exit. The text will be written in test2 file. You can see contains of file with following cat command.
# cat test2 hello everyone, how do you do?
4. Use Cat Command with More & Less Options
If file having large number of contains that won’t fit in output terminal and screen scrolls up very fast, we can use parameters more and less with cat command as show above.
# cat song.txt | more # cat song.txt | less
5. Display Line Numbers in File
With -n option you could see the line numbers of a file song.txt in the output terminal.
# cat -n song.txt 1 "Heal The World" 2 There's A Place In 3 Your Heart 4 And I Know That It Is Love 5 And This Place Could 6 Be Much 7 Brighter Than Tomorrow 8 And If You Really Try 9 You'll Find There's No Need 10 To Cry 11 In This Place You'll Feel 12 There's No Hurt Or Sorrow
6. Display $ at the End of File
In the below, you can see with -e option that ‘$‘ is shows at the end of line and also in space showing ‘$‘ if there is any gap between paragraphs. This options is useful to squeeze multiple lines in a single line.
# cat -e test hello everyone, how do you do?$ $ Hey, am fine.$ How's your training going on?$ $
7. Display Tab separated Lines in File
In the below output, we could see TAB space is filled up with ‘^I‘ character.
# cat -T test hello ^Ieveryone, how do you do? Hey, ^Iam fine. ^I^IHow's your training ^Igoing on? Let's do ^Isome practice in Linux.
8. Display Multiple Files at Once
In the below example we have three files test, test1 and test2 and able to view the contains of those file as shown above. We need to separate each file with ; (semi colon).
# cat test; cat test1; cat test2 This is test file This is test1 file. This is test2 file.
9. Use Standard Output with Redirection Operator
We can redirect standard output of a file into a new file else existing file with ‘>‘ (greater than) symbol. Careful, existing contains of test1 will be overwritten by contains of test file.
# cat test > test1
10. Appending Standard Output with Redirection Operator
Appends in existing file with ‘>>‘ (double greater than) symbol. Here, contains of test file will be appended at the end of test1 file.
# cat test >> test1
11. Redirecting Standard Input with Redirection Operator
When you use the redirect with standard input ‘<‘ (less than symbol), it use file name test2 as a input for a command and output will be shown in a terminal.
# cat < test2 This is test2 file.
12. Redirecting Multiple Files Contain in a Single File
This will create a file called test3 and all output will be redirected in a newly created file.
# cat test test1 test2 > test3
13. Sorting Contains of Multiple Files in a Single File
This will create a file test4 and output of cat command is piped to sort and result will be redirected in a newly created file.
# cat test test1 test2 test3 | sort > test4
This article shows the basic commands that may help you to explore cat command. You may refer man page of cat command if you want to know more options. In out next article we will cover more advanced cat commands. Please share it if you find this article useful through our comment box below.
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