A command is the set of programs that perform some particular task in a computer's system. It triggers when a user do any work or perform some particular task.
Below be describe some UNIX shell based commands
ls -l -t -r /bin
ls -ltr /bin
The following command displays the contents of the files. The cat command derived from the word concatenation. It concatenates file2 to file1.
cat file1.txt file2.txt