Basic file manipulation with the cat command

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Here we’ll use the cat command to display, create, and concatenate files. This command is useful when you do complex data wrangling.

The cat command is one of the most basic yet useful commands for working with files. It has three main functions when it comes to text files: display their content, create new files, and combine copies.

Display content

The cat command is most commonly used to read the content of files. Its default output destination, which is also known as a standard output, or stdout, is the monitor screen. To display the content of a file, you would input cat <filename>.

Run the cat command to display the contents of NASA-software-API.txt.BashCopy

cat NASA-software-API.txt

Create files

You can use the cat command to create files. Using this command is often easier than using a vi or text editor for small files.

Create new files by redirecting the standard output of the cat command by using the output redirect operator > followed by the name of the file to be created. Then select ENTER, and finally simultaneously select CTRL+D.

1. Run the cat command followed by the > operator and the file name, file1.BashCopycat > file1
2. Select ENTER to place the cursor at a new line.
3. Enter some text, in this case, NASA headquarters. Then select ENTER.
4. End the program and restore the command prompt by selecting CTRL+D. If file1 exists, it will be overwritten.
5. To append a line to the existing file without overwriting, you can use the >> operator. For example, to add Goddard Space Flight Center to file1 you would first run:BashCopycat >> file1
6. Select ENTER, and then add the next line:BashCopyGoddard Space Flight Center
7. Select ENTER, then CTRL+D to complete the command.

Concatenate files

The third use of the cat command is to concatenate copies of the contents of files. Because the concatenation occurs only to the copies, there’s no effect on the original files.

For example, to concatenate two copies of the file1 we created before, you would run the following command:BashCopy

cat file1 file1

Your output should look something like this:OutputCopy

NASA headquarters
Goddard Space Flight Center
NASA headquarters
Goddard Space Flight Center

If you run the command ls again, you’ll see that the new files have been added to your directory:OutputCopy

file1 NASA-logs-1995.txt NASA-software-API.txt

The contents of each file will be displayed on the stdout starting on a new line and in the order that the file names appear in the command. You can also redirect this output to a second file, file2.BashCopy

cat file1 file1 > file2