Viewing Files In Linux

There are a few Linux commands available to view the content of files. The cat command, which stands for “concatenate”, is often used to quickly view the contents of small files.

The cat command will display the entire contents of the file, hence why it is mainly recommended for smaller files where the output is limited and does not require scrolling. To view the contents of a file using the cat command, simply type the command and use the name of the file you wish to view as the argument:

cat [OPTIONS] [FILE]

Our VM has a few small text files that you can view with the cat command. One such file is the animals.txt file:

Follow Along

Use the following command to switch to the Documents directory:

sysadmin@localhost:~$ cd ~/Documents

sysadmin@localhost:~/Documents$ cat animals.txt                            
1 retriever                                                             
2 badger                                                                
3 bat                                                                  
4 wolf                                                                  
5 eagle

The cat command displays all five lines of the file above. When viewing larger files, the cat command can result in very lengthy output that cannot be paused to scroll through. A better method of viewing long text files, is with a pager command which has a functionality that can pause and scroll through the output of the file.

Note

Examples of pager commands include the more and less commands. These and additional commands used for viewing files in Linux are covered in NDG Linux Essentials.

Another way to view the content of files is by using the head and tail commands. These commands are used to view a select number of lines from the top or bottom of a file. Taking a look at a few lines of a file can sometimes be helpful to ensure that the file is the one you want to use.

Another reason to preview only the first or last few lines, is because some files, such as system log files are frequently updated with new entries. Similar to the cat command, the head and tail commands use the name of the file you want to view as the argument to the command:

head [OPTIONS] [FILE]

tail [OPTIONS] [FILE]

To compare the output of the head and tail commands with that of the cat command, use the cat command to view the entire alpha.txt file:

sysadmin@localhost:~/Documents$ cat alpha.txt       
A is for Apple                    
B is for Bear           
C is for Cat                      
D is for Dog                               
E is for Elephant                                      
F is for Flower       
G is for Grapes                     
H is for Happy                                     
I is for Ink                                                         
J is for Juice                                   
K is for Kangaroo
L is for Lol                                                             
M is for Monkey                       
N is for Nickel                             
O is for Oval                  
P is for Pickle       
Q is for Quark                         
R is for Rat                          
S is for Sloth                       
T is for Turnip                        
U is for Up                                     
V is for Velvet                       
W is for Walrus                    
X is for Xenon                        
Y is for Yellow         
Z is for Zebra           
sysadmin@localhost:~/Documents$

In the example above, all twenty-six lines of the file are displayed.

To filter the output and view lines from the top of the alpha.txt file, use the head command:

sysadmin@localhost:~/Documents$ head alpha.txt                          
A is for Apple                                                        
B is for Bear                                                         
C is for Cat                                                        
D is for Dog                                                         
E is for Elephant                                                     
F is for Flower                                                       
G is for Grapes                                                        
H is for Happy                                                        
I is for Ink                                                          
J is for Juice

Then, to view lines at the bottom of the alpha.txt file, you use the tail command:

sysadmin@localhost:~/Documents$ tail alpha.txt                          
Q is for Quark                                                         
R is for Rat                                                           
S is for Sloth                                                        
T is for Turnip                                                        
U is for Up                                                            
V is for Velvet                                                      
W is for Walrus                                                        
X is for Xenon                                                        
Y is for Yellow                                                        
Z is for Zebra

By examining the output of the head and tail commands above, you can see that the default behavior of the head and tail commands in this shell is to display ten lines.

The -n option with the head and tail commands can be used to specify the amount of lines to display. To use the -n option, specify the amount of lines from the file you want to display after the option and use the filename as an argument:

head -n number_of_lines filename

For example, to change the output of the head command to view the first five lines of the alpha.txt file:

sysadmin@localhost:~/Documents$ head -n 5 alpha.txt                    
A is for Apple                                                         
B is for Bear                                                          
C is for Cat                                                           
D is for Dog                                                           
E is for Elephant

View the last five lines of the alpha.txt file:

sysadmin@localhost:~/Documents$ tail -n 5 alpha.txt 
V is for Velvet                                                        
W is for Walrus                                                         
X is for Xenon                                                          
Y is for Yellow                                                         
Z is for Zebra            
sysadmin@localhost:~/Documents$