cat command would be on your fingers without any restriction or hesitation if you are going to be a Linux user, In other words, you can say “cat command is most used command in Linux”. You must know the first basic syntax of cat command in Linux.
Generally, cat utility in Linux is used to display the content of the file. I can’t stop me to use cat command at the time to peep into the file.
It is not just used only for a single purpose to see the content of the file, but you can use the cat command to create a file in Linux. I will share the basic syntax of cat tool in Linux.
The basic syntax of cat command
Content Article:
- The basic syntax of cat command
- Use the cat command to create a file in Linux
- Use the cat command to add content in the file
- Use the cat command to display contents of File
- Display Line Numbers in File
- Display $ at the End of File
- Display Tab-separated Lines in File
- View Contents of Multiple Files by this command
- Copy content from one file to another
- Copy content of multiple files in a single file
- Sorting Contents of Multiple Files in a Single File
The basic syntax of cat command in Linux
We all must know about the basics fo cat command, you can use the man for displaying manual so you can know more about it.
Use the following syntax to know more:
$man cat
When you follow the above step, you will able to find out the basic syntax of cat command.
I am going to share with you, it is as follows:
cat [OPTION] [FILE]…
Use the cat command to create a file in Linux
Let’s start our first task, create a file in Linux by using cat command, It is a very simple option to perform this action:
Syntax as follows if you want to create a file inside the current working directory otherwise give the directory location where you want to create a file.
$cat > filename
$cat > /Path/to/directory/filename
I am going to create a file in the current directory in the first example and in the second example I will create a file inside /home/vijay/Documents
[vijay@localhost ~]$ ls Desktop Documents Downloads Music Pictures Public Templates Videos [vijay@localhost ~]$ cat file1 cat: file1: No such file or directory [vijay@localhost ~]$ cat >file1 This is the file 1 I want to add something in this file later [vijay@localhost ~]$
I the above example I have used “ls” command to see the content inside current directory.
Later I used “cat file1” to see the available content inside file1, but I got error result as you can see above.
Next I used command “cat >file1” Then I wrote 2 lines, You can write as long as you want. When you complete your writing Press “Ctrl +d” to save and exit.
Again you can use ls command
Use the cat command to add content in the file
You can use >> instead of > followed by the filename.
[vijay@localhost ~]$ cat >>file1 This is the second line in file1 this is the third line in file1 [vijay@localhost ~]$
I have added two lines again by using “cat>>file1” command. Pressed “Ctrl+d” to save and exit from file.
Use the cat command to display contents of File
As you saw “I have created a file and write some content”. But how will I check the content exist inside file1.
Yes, It is time to peep into file1. Here is the command:
$cat filename
[vijay@localhost ~]$ cat file1 This is the file 1 I want to add something in this file later This is the second line in file1 this is the third line in file1 [vijay@localhost ~]$
Display Line Numbers in File
I created a file with only 4 lines, but you can add multiple. Even you can imagine, a programing file has lots of lines. If you want to go on particular line, you must display the number of lines.
$ cat -n filename
[vijay@localhost ~]$ cat -n file1
1 This is the file 1
2 I want to add something in this file later
3 This is the second line in file1
4 this is the third line in file1
[vijay@localhost ~]$
I am going to show you another example:
[vijay@localhost ~]$ cat -n /etc/passwd
1 root:x:0:0:root:/root:/bin/bash
2 bin:x:1:1:bin:/bin:/sbin/nologin
3 daemon:x:2:2:daemon:/sbin:/sbin/nologin
4 adm:x:3:4:adm:/var/adm:/sbin/nologin
5 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
6 sync:x:5:0:sync:/sbin:/bin/sync
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
8 halt:x:7:0:halt:/sbin:/sbin/halt
9 mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
10 operator:x:11:0:operator:/root:/sbin/nologin
11 games:x:12:100:games:/usr/games:/sbin/nologin
12 ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
13 nobody:x:65534:65534:Kernel Overflow User:/:/sbin/nologin
14 dbus:x:81:81:System message bus:/:/sbin/nologin
15 systemd-coredump:x:999:997:systemd Core Dumper:/:/sbin/nologin
16 systemd-resolve:x:193:193:systemd Resolver:/:/sbin/nologin
17 tss:x:59:59:Account used by the trousers package to sandbox the tcsd daemon:/dev/null:/sbin/nologin
18 polkitd:x:998:996:User for polkitd:/:/sbin/nologin
19 geoclue:x:997:995:User for geoclue:/var/lib/geoclue:/sbin/nologin
20 rtkit:x:172:172:RealtimeKit:/proc:/sbin/nologin
21 pulse:x:171:171:PulseAudio System Daemon:/var/run/pulse:/sbin/nologin
22 qemu:x:107:107:qemu user:/:/sbin/nologin
23 usbmuxd:x:113:113:usbmuxd user:/:/sbin/nologin
24 unbound:x:996:991:Unbound DNS resolver:/etc/unbound:/sbin/nologin
25 rpc:x:32:32:Rpcbind Daemon:/var/lib/rpcbind:/sbin/nologin
26 gluster:x:995:990:GlusterFS daemons:/run/gluster:/sbin/nologin
27 chrony:x:994:989::/var/lib/chrony:/sbin/nologin
28 libstoragemgmt:x:993:987:daemon account for libstoragemgmt:/var/run/lsm:/sbin/nologin
29 pipewire:x:992:986:PipeWire System Daemon:/var/run/pipewire:/sbin/nologin
30 saslauth:x:991:76:Saslauthd user:/run/saslauthd:/sbin/nologin
31 setroubleshoot:x:990:985::/var/lib/setroubleshoot:/sbin/nologin
32 dnsmasq:x:984:984:Dnsmasq DHCP and DNS server:/var/lib/dnsmasq:/sbin/nologin
33 radvd:x:75:75:radvd user:/:/sbin/nologin
34 clevis:x:983:982:Clevis Decryption Framework unprivileged user:/var/cache/clevis:/sbin/nologin
35 cockpit-ws:x:982:980:User for cockpit-ws:/nonexisting:/sbin/nologin
36 sssd:x:981:979:User for sssd:/:/sbin/nologin
37 colord:x:980:978:User for colord:/var/lib/colord:/sbin/nologin
38 gdm:x:42:42::/var/lib/gdm:/sbin/nologin
39 rpcuser:x:29:29:RPC Service User:/var/lib/nfs:/sbin/nologin
40 gnome-initial-setup:x:979:977::/run/gnome-initial-setup/:/sbin/nologin
41 sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
42 avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin
43 tcpdump:x:72:72::/:/sbin/nologin
44 vijay:x:1000:1000:Vijay Kumar:/home/vijay:/bin/bash
45 vboxadd:x:978:1::/var/run/vboxadd:/bin/false
[vijay@localhost ~]$
Display $ at the End of File
Sometime, You are writing a long paragraph without hitting enter button.
$ sign will be displayed at the end of line as well as gap between two paragraphs
[vijay@localhost ~]$ cat >file2 Hi friends, how are you? Hey, I am fine. I hope you are doing well. How's your training and study going on? [vijay@localhost ~]$ cat -e file2 Hi friends, how are you?$ $ Hey, I am fine.$ I hope you are doing well.$ $ How's your training and study going on?$ $ [vijay@localhost ~]$
First, I have created a new file with name file2 by using cat command later I have displayed same file with $ end of line.
Display Tab-separated Lines in File
You can use cat command followed by “T” options to display tab seperated lines.
Syntax of cat command for displaying tab separated lines are below:
$cat -T filename
View Contents of Multiple Files by this command
Do you want to view multiple files at once? then this section is very useful.
You can use following command to view multiple files:
cat firstfilename; cat secondfilename; cat thirdfilename
[vijay@localhost ~]$ cat file1; cat file2 This is the file 1 I want to add something in this file later This is the second line in file1 this is the third line in file1 Hi friends, how are you? Hey, I am fine. I hope you are doing well. How's your training and study going on? [vijay@localhost ~]$
Copy content from one file to another
Cat command in linux is used to display content on the screen, it happend due standard output.
We can redirect standard output into file by using “>” character.
So you can copy one file to another file by using this command.
See the example below:
cat file1 > newfile1
[vijay@localhost ~]$ cat file1 >newfile1 [vijay@localhost ~]$ cat newfile1 This is the file 1 I want to add something in this file later This is the second line in file1 this is the third line in file1 [vijay@localhost ~]$
If you want to add content inside existing file then use “>>” operator followed by newfilename
$cat file1 >>newfilename
Copy content of multiple files in a single file
It is similar display multiple files first as output and redirect to another newfile2
$cat file1 file2; >newfile2
[vijay@localhost ~]$ cat file1 file2 >newfile2 [vijay@localhost ~]$ cat newfile2 This is the file 1 I want to add something in this file later This is the second line in file1 this is the third line in file1 Hi friends, how are you? Hey, I am fine. I hope you are doing well. How's your training and study going on? [vijay@localhost ~]$
Sorting Contents of Multiple Files in a Single File
You can use sort pipe operator to sort output of multiple file’s content.
Example:
$cat file1 file2 | sort >newfile3
[vijay@localhost ~]$ cat file1 file2 |sort >newfile3 [vijay@localhost ~]$ cat newfile3 Hey, I am fine. Hi friends, how are you? How's your training and study going on? I hope you are doing well. I want to add something in this file later This is the file 1 This is the second line in file1 this is the third line in file1 [vijay@localhost ~]$
Conclusion
This article shows the basic syntax of cat command in Linux that may help you to explore cat command. You have learnt using basic syntax of cat tool in Linux to create file and edit files.
As I have told you already You may refer man page of cat command if you want to know more options.
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