Learn Linux Shell Scripting - Fundamentals of Bash 4.4

Redirecting redirections

We already gave you a sneak preview of the process of redirecting redirections. The most famous example, which was mostly used before Bash 4.x, is redirecting the stderr stream to the stdout stream. By doing this, you can redirect all output with just the > syntax.

You can achieve it like this:

reader@ubuntu:/tmp$ cat /etc/shadowcat: /etc/shadow: Permission deniedreader@ubuntu:/tmp$ cat /etc/shadow > shadowcat: /etc/shadow: Permission deniedreader@ubuntu:/tmp$ cat shadow #Still empty, since stderr wasn't redirected to the file.reader@ubuntu:/tmp$ cat /etc/shadow > shadow 2>&1 #Redirect fd2 to fd1 (stderr to stdout).reader@ubuntu:/tmp$ cat shadow cat: /etc/shadow: Permission denied

Remember, you no longer need this ...