18.3-redirection.txt

18.3. stdout to screen

The simple way to redirect a standard output ( stdout ) is to simply use any command, because by default stdout is automatically redirected to screen. First create a file "file1":

$ touch file1
$ ls file1 
file1

As you can see from the example above execution of ls command produces STDOUT which by default is redirected to screen.
18.4. stdout to file

The override the default behavior of STDOUT we can use ">" to redirect this output to file:

$ ls file1 > STDOUT
$ cat STDOUT 
file1

18.5. stderr to file

By default STDERR is displayed on the screen:

$ ls
file1  STDOUT
$ ls file2
ls: cannot access file2: No such file or directory

In the following example we will redirect the standard error ( stderr ) to a file and stdout to a screen as default. Please note that STDOUT is displayed on the screen, however STDERR is redirected to a file called STDERR:

$ ls
file1  STDOUT
$ ls file1 file2 2> STDERR
file1
$ cat STDERR 
ls: cannot access file2: No such file or directory

18.6. stdout to stderr

It is also possible to redirect STDOUT and STDERR to the same file. In the next example we will redirect STDOUT to the same descriptor as STDERR. Both STDOUT and STDERR will be redirected to file "STDERR_STDOUT".

$ ls
file1  STDERR  STDOUT
$ ls file1 file2 2> STDERR_STDOUT 1>&2
$ cat STDERR_STDOUT
ls: cannot access file2: No such file or directory
file1

File STDERR_STDOUT now contains STDOUT and STDERR.
18.7. stderr to stdout

The above example can be reversed by redirecting STDERR to the same descriptor as SDTOUT:

$ ls
file1  STDERR  STDOUT
$ ls file1 file2 > STDERR_STDOUT 2>&1
$ cat STDERR_STDOUT 
ls: cannot access file2: No such file or directory
file1

18.8. stderr and stdout to file

Previous two examples redirected both STDOUT and STDERR to a file. Another way to achieve the same effect is illustrated below:

$ ls
file1  STDERR  STDOUT
$ ls file1 file2 &> STDERR_STDOUT
$ cat STDERR_STDOUT 
ls: cannot access file2: No such file or directory
file1

or

ls file1 file2 >& STDERR_STDOUT
$ cat STDERR_STDOUT 
ls: cannot access file2: No such file or directory
file1