Cat(concatenate) command is an excellent command used to view files. This will conCATenate(Combines two are more files) and display it’s content on the screen. Cat command not only display the file content but it can also do merging files , creating files sending one file to other file etc. Lets learn cat command with with practical examples first and then with  some  options .
Example 1: Display file content on stranded output (STDOUT)

cat filename.txt

cat < filename.txt

Example 2: Send the file content as input to other command. For example count number of lines in a file

cat filename.txt | wc -l

Example 3: Create a file using cat. execute below command start typing the contents on the screen/at terminal once you enter your data, save the file by pressing ctrl+d

cat > filename.txt
(press ctrl+d)

Example 4: Copy one file content to other(over write the file)

cate file1.txt > file2.txt

<, >, | operators etc are called as redirect operators here redirect operators with examples

Example 5:
Copy one file content to other (don’t overwrite but append it)

cat file1.txt >> file2.txt

Example 6: Copy 2 files in to third file(overwrite if the third file exists)

cat file1.txt file2.txt > file3.txt


cat file{1,2}.txt > file3.txt

learn more about {} braces 

Example 7: Copy 2 files in to third file(append the date to third file)

cat file1.txt file2.txt >> file3.txt

Example  8: To copy file abc.txt and write some date using keyboard then redirecting both to a file called xyz.txt.

cat - abc.txt > xyz.txt
cat abc.txt - > xyz.txt

Note: The first command will write keyboard typed date first to file xyz.txt then abc.txt to xyz.txt. Where as the command first abc.txt data is written to xyz.txt then followed with the data entered from keyboard.

Example 9: Display the file content along with number of the line or number the line numbers using cat command

cat -n filename.txt

Example 10: Display file content along with numbers for lines with data

cat -b filename.txt

Example 11: Hide repeated empty lines when displaying content of the file.

cat -s filename.txt

Note: This command will display single empty line for a sequence of multiple empty lines.

Example 12: Display tabs in a file using cat command

cat -t filename.txt

There are many more cat command options which we can get through manual pages.

whatis cat
man cat
info cat

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