Linux Cat Command Examples

Cat is a standard unix tool to concatenate and display the content of files. In this post, I will present some examples of cat command so that you can use them in your scenario.

The cat command displays the content of file on the standard output. If multiple files are specified, the contents of all files will be concatenated and then displayed on the standard output. Likewise, if no file is specified, it will assume standard input (keyboard input) as the input to the command. The Ctrl + d is the shortcut used to save the contents in the appropriate output placeholder specified and exit the cat command.

Print content of file in standard output

samar@samar-Techgaun:~$ cat workers.txt 
List of workers, designations & salary (in K):
Kshitiz Director 30
Bikky Manager  20


Abhis Sweeper  10
Rajesh Guard  12

Print line numbers

samar@samar-Techgaun:~$ cat -n workers.txt 
     1 List of workers, designations & salary (in K):
     2 Kshitiz Director 30
     3 Bikky Manager  20
     4 
     5 
     6 Abhis Sweeper  10
     7 Rajesh Guard  12

Print line numbers for non-empty lines only

samar@samar-Techgaun:~$ cat -b workers.txt 
     1 List of workers, designations & salary (in K):
     2 Kshitiz Director 30
     3 Bikky Manager  20


     4 Abhis Sweeper  10
     5 Rajesh Guard  12

Create a new file

samar@samar-Techgaun:~$ cat > newfile.txt
We can create text files
using cat command
once u finish writing,
press ctrl+d to save file
^d

Display content of multiple files

samar@samar-Techgaun:~$ cat workers.txt newfile.txt 
List of workers, designations & salary (in K):
Kshitiz Director 30
Bikky Manager  20


Abhis Sweeper  10
Rajesh Guard  12
We can create text files
using cat command
once u finish writing,
press ctrl+d to save file

Combine multiple files to new file

samar@samar-Techgaun:~$ cat workers.txt newfile.txt > concat.txt
samar@samar-Techgaun:~$ cat concat.txt 
List of workers, designations & salary (in K):
Kshitiz Director 30
Bikky Manager  20


Abhis Sweeper  10
Rajesh Guard  12
We can create text files
using cat command
once u finish writing,
press ctrl+d to save file

Append data to existing file

samar@samar-Techgaun:~$ cat >> newfile.txt 
New line added
^d
samar@samar-Techgaun:~$ cat newfile.txt 
We can create text files
using cat command
once u finish writing,
press ctrl+d to save file
New line added

Alternatively, you can use the syntax below if you wish to create new file combining the content of already existing file and standard input.

samar@samar-Techgaun:~$ cat newfile.txt - > myfile
thanks for everything
^d
samar@samar-Techgaun:~$ cat myfile 
We can create text files
using cat command
once u finish writing,
press ctrl+d to save file
New line added
thanks for everything

Another possibility is to combine two text files with data from standard input (keyboard) in-between the contents of these two text files.

samar@samar-Techgaun:~$ cat workers.txt - newfile.txt > myfile

----------------------------------

^d
samar@samar-Techgaun:~$ cat myfile 
List of workers, designations & salary (in K):
Kshitiz Director 30
Bikky Manager  20


Abhis Sweeper  10
Rajesh Guard  12

----------------------------------

We can create text files
using cat command
once u finish writing,
press ctrl+d to save file
New line added

Display $ sign at the end of each line

samar@samar-Techgaun:~$ cat -E workers.txt 
List of workers, designations & salary (in K):$
Kshitiz Director 30$
Bikky Manager  20$
$
$
Abhis Sweeper  10$
Rajesh Guard  12$

Display ^I sign instead of TABs

samar@samar-Techgaun:~$ cat -T workers.txt 
List of workers, designations & salary (in K):
Kshitiz^IDirector^I30
Bikky^IManager^I^I20


Abhis^ISweeper^I^I10
Rajesh^IGuard^I^I12

Display files with non-printing characters

samar@samar-Techgaun:~$ cat -v /bin/nc

In the example above, the non-printing characters are replaced with ^ and M- notation except for line breaks and TABs. This can be used to display the contents of binary files which would otherwise have shown gibberish text all over the console.

Show contents with tabs, line breaks and non-printing characters

samar@samar-Techgaun:~$ cat -A /bin/nc

The tab will be substituted by ^I, line breaks with $ and non-printing characters with ^ and M- notation. Actually, the -A switch is equivalent to -vET switch.

Supress/squeeze repeated empty lines

samar@samar-Techgaun:~$ cat -s workers.txt 
List of workers, designations & salary (in K):
Kshitiz Director 30
Bikky Manager  20

Abhis Sweeper  10
Rajesh Guard  12

Using -s switch, we can squeeze repeatedly occurring blank lines and replace all the adjacent empty lines with a single empty line in the output. This might be useful to reformat a file with several empty lines in-between (eg. cat -s workers.txt > formatted_workers.txt).

Display last line first

samar@samar-Techgaun:~$ tac workers.txt 
Rajesh Guard  12
Abhis Sweeper  10

Bikky Manager  20
Kshitiz Director 30
List of workers, designations & salary (in K):

It is the tac, not the cat that is doing the magic but just thought that this is the right place to make a note about this little known command.

Edit: Added here-doc examples. Thanks rho dai for pointing me this.

Parameter substitution using here-document strings

samar@samar-Techgaun:~$ cat > test << TEST
samar@samar-Techgaun:~$ I am $USER. My home is $HOME
samar@samar-Techgaun:~$ I came here from $OLDPWD
samar@samar-Techgaun:~$ TEST
samar@samar-Techgaun:~$ cat test 
I am samar. My home is /home/samar
I came here from /home/samar/Downloads

Command expansion example

samar@samar-Techgaun:~$ cat > test << TEST
samar@samar-Techgaun:~$ $(ls /)
samar@samar-Techgaun:~$ TEST
samar@samar-Techgaun:~$ cat test
bin
boot
cdrom
dev
etc
home
initrd.img
initrd.img.old
lib
lost+found
media
mnt
opt
proc
root
run
sbin
selinux
srv
sys
tmp
usr
var
vmlinuz
vmlinuz.old

Parameter substitution turned off

samar@samar-Techgaun:~$ cat > test << 'TEST'
samar@samar-Techgaun:~$ I am $USER. My home is $HOME
samar@samar-Techgaun:~$ I came here from $OLDPWD
samar@samar-Techgaun:~$ TEST
samar@samar-Techgaun:~$ cat test
I am $USER. My home is $HOME
I came here from $OLDPWD

Note the difference between the last example and previous two examples. Enclosing the limit string TEST with quotes prevents the substitutions and expansions.

I hope these examples are useful. :)


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Ubuntu Tweak Development Will Continue

Three days ago, Ubuntu Tweak developer Tualatrix had posted a blog post mentioning that the Ubuntu Tweak will no longer be developed but he has now changed his mind and has decided to continue the development because of support he received.

The developer writes
You made me know that Ubuntu Tweak is still valuable, and as the first software project I made 5 years ago, it is just like my baby, I don’t really want to give up the development.

and thanks all the good people who left the message for him and forked the app in github.

The blog post also mentions
Back to 5 years ago, I developed it just because of my practice on Linux programming, I felt freedom when I make things on Linux (Although I didn’t have developing experience on Windows and Mac then). But now I don’t feel any freedom about developing this software any more. The initial motivation is changed, and I’m still looking for new motivation.

Overall, he is not too satisfied with his current overload for working on this personal project while still managing time for his job and personal life.

Anyway, Ubuntu Tweak 0.8.1 is out and you can download from PPA.

PPA DEB link

Release Notes


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Enable Auto Correction Of Path In Bash

While using the cd command, its normal to make mistakes while typing the directory path. You can enable auto-correction while typing directory path by enabling a particular shell option.

Minor spelling mistakes will be corrected automatically if the particular shell option cdspell using the SHell OPTions command invoked with shopt command.

When you enable the cdspell shell option, the errors checked for are missing characters, repeated characters, and transposed characters. Once the error is encountered, the corrected path is printed and directory is changed successfully.

samar@samar-Techgaun:~$ shopt -s cdspell
samar@samar-Techgaun:~$ cd Desktp
Desktop
samar@samar-Techgaun:~/Desktop$ cd ../Deskotp/
../Desktop/
samar@samar-Techgaun:~/Desktop$ cd ../Desktoop
../Desktop
samar@samar-Techgaun:~/Desktop$

The line shopt -s cdspell enables the auto-correction while using cd command. The session above shows some of the corrections performed once we enabled the cdspell shell option.

If you want to turn on this particular setting, then add the appropriate line using the command below:

samar@samar-Techgaun:~$ echo "shopt -s cdspell" >> ~/.bash_profile

I hope this counts as useful tips to beginner linux guys ;)


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Ubuntu Tweak Will No Longer Be Developed

Comes as a very sad news but Ubuntu Tweak developer has decided to stop the development of Ubuntu Tweak. Tualatrix Chou writes in a blog post:

" I want to stop the development and maintenance of Ubuntu Tweak. This means you will not be able to use “Apps” (Since it is a web service), I will not response for the bug report, the last commit of the code will be: Add cache support for Apps, only available in Ubuntu 12.10, so sad".

While the developer writes the reason as If making free software is not free any more, why still doing this?, I found the whole post quite cryptic.

One of his friend mentions that Ubuntu Tweak, though being a great app has not been included in the official source which is a really depressing thing.


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Practical ls Command Examples For Fun & Profit

The power of linux lies in the shell through which we can perform complex job in no time. While the directory listing command 'ls' seems to be very simple command, the linux shell provides the power to use switches and pipes to do anything from terminal. Check out this list with practically useful examples using ls.

Display all files including hidden files/folders

ls -a

Display one file/folder per line

ls -1

Count number of files & folders

ls -1 | wc -l

Human readable file sizes (eg. Mb or Gb)

ls -lh

Alphabetically sort the listing

ls -X

Only list the folders in current directory

ls -d */
ls -p | grep /

Display folders in current directory consisting certain patterns

ls -l D* | grep :$
ls -l *a* | grep :$

List files by descending order of modification time

ls -lt
ls -l --sort=time #alternative long version

List files by descending order of creation time

ls -lct

List files in reverse order

ls -ltr
ls -l --sort=time --reverse #alternative long version

List files in descending order of file size

ls -lSh
ls -lh --sort=size
ls -lSh1 *.avi #find largest AVI file
rm `ls -S1 | head -1` #delete largest file in current folder

List files in ascending order of file size

ls -lShr
ls -lh --sort=size --reverse #alternative long version

Display directories in recursive manner

ls -R

Display the files/folders created today

ls -l --time-style=+%F | grep `date +%F`

Display the files/folders created this year

ls -l --time-style=+%y | grep `date +%y`

Any more example that fires up in your mind? Feel free to share over here ;)


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Useful Nautilus Shortcuts

Nautilus is a default file manager for GNOME Desktop and is used as the default file manager in several linux distros such as Ubuntu. I love nautilus because its simple, friendly, and clean, supports local as well as remote file systems over different protocols. Moreover, there are several useful shortcuts that make life easier while using nautilus.

Below is the list of the most helpful shortcuts for navigation and file management in the nautilus:

Ctrl + r: Refresh the current view

Ctrl + h: Toggle show/hide mode for hidden files

F9: Show/Hide the side pane

Ctrl + l: Activate location/url bar (You can then provide path to local or remote filesystems or quickly copy the absolute paths)

Alt + Up Arrow: Move up one directory level

Alt + Down Arrow: Move down one directory level (the directory to be entered should be selected for this to work)

Alt + Left Arrow: Go back to the previous folder in view

Alt + Right Arrow: Go forward

Ctrl + Shift + n: Create a new empty directory

Ctrl + (+ / -): Zoom in (+) or zoom out (-)

Ctrl + 0: Zoom to normal state

Alt + Enter: View selected file/folder properties

F2: Rename selected file/folder

Ctrl + Shift + Drag file/folder: Create symbolic link to file/folder

Ctrl + f: Search for files/folders

Ctrl + s: Select files based upon templates (eg. select all pdf files using *.pdf)

Ctrl + 1: Toggle view as icons

Ctrl + 2: Toggle view as lists

Ctrl + 3: Toggle compact view

Ctrl + w: Close current nautilus window

Ctrl + Shift + w: Current all open nautilus windows

Ctrl + T: Open new tab

Alt + HOME: Navigate to HOME folder

F6: Toggle between side pane and central pane

Know more shortcuts? Share as the comments :)


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Empty Trash From Command Line In Ubuntu

CLI is such a sexy piece so why bother using GUI, even for cleaning up your trash. In this post, you will see how you can empty trash in Ubuntu from command line.

The trash you see in GUI is nothing but just the view for the files deleted by users which are temporarily moved to the special location of user's home directory. For any user, the trash location is ~/.local/share/Trash/. That is, whatever a user deletes gets saved in this location.

samar@samar-Techgaun:~$ rm -rf ~/.local/share/Trash/

I hope this becomes useful :)


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Enable Fingerprint Authentication In Ubuntu

So you got fingerprint reader in your device but have not been able to use it under ubuntu? Follow this How To to enable fingerprint authentication in ubuntu using the Fingerprint GUI from fingerprints reader integration team.

First make sure your fingerprint hardware is supported. You can check for the vendor and device ID by entering the following command:

samar@TG:~$ lsusb | grep -i finger | awk -F " " '{print $6}'
138a:0005

This link provides the list of the supported fingerprint readers.

Installation is easy. Fire up the terminal and enter the following commands:

sudo add-apt-repository ppa:fingerprint/fingerprint-gui
sudo apt-get update
sudo apt-get install libbsapi policykit-1-fingerprint-gui fingerprint-gui

You will have to restart the system or log out the session and login back to use and configure the fingerprint GUI.

Press Alt + F2 and type fingerprint-gui. From this GUI, you can configure and enroll your fingerprints.

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