sterr

The stardard stream where errors are logged out to avoid conflicts with stdout.

$ ls /non-existent/directory > test.txt
ls: cannot access /fake/directory: No such file or directory
$ cat test.txt # outputs nothing

We have to redirect it with the 2> Bash Stream Redirection operator.

if we want to redirect or append both stdout and stderr, we use &> or &>>, respectively.

$ ls /fake/directory 2> test.txt
$ cat test.txt
ls: cannot access '/fake/directory': No such file or directory