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