There are some situations where you can get both standard output and an error message at the same time. For example, if you run the following command:
elliot@ubuntu-linux:~$ cat planets.txt blabla
Saturn is a planet.
Mars is a planet.
Venus is a planet.
cat: blabla: No such file or directory
You will see that it displayed the contents of the file planets.txt, but it also displayed an error message at the very last line (because there is no file blabla to concatenate).
You can choose to redirect the error to another file:
elliot@ubuntu-linux:~$ cat planets.txt blabla 2> err.txt
Saturn is a planet.
Mars is a planet.
Venus is a planet.
This way, you only see the standard output on the screen. Or you may choose to redirect the standard output:
elliot@ubuntu-linux:~$ cat planets.txt blabla 1> output.txt
cat: blabla: No such file or directory
This way, you only see the error on the screen. Now, what if you want to redirect both the standard output...
