To concatenate text files in Ubuntu Linux, you can use the cat command. Here is an example:
cat file1.txt file2.txt > file3.txt
This command will concatenate the contents of file1.txt and file2.txt and save the result in a new file called file3.txt.
You can also use the cat command to concatenate multiple files and display the result on the screen, like this:
cat file1.txt file2.txt
In this example, the contents of file1.txt and file2.txt will be displayed on the screen.