`

|

Redirects output of a command as input to another command

Let’s practice using redirection operators to see how they work

with standard streams. The > operator redirects the standard output

stream to a file. Any command that precedes this character will send

its output to the specified location. Run the following command

directly in your terminal:

$ echo "Hello World!" > output.txt

We redirected the standard output stream to a file named

output.txt. To see the content of output.txt, simply run the following:

$ cat output.txt

Hello World!

Next, we’ll use the >> operator to append some content to the

end of the same file:

$ echo "Goodbye!" >> output.txt

$ cat hello_output.txt

Hello World!

Goodbye!

Listing 1-10

Append text to a file

If we used > instead of >>, the content of output.txt would have

been overwritten completely with the Goodbye! text.

You can redirect both the standard output stream and the

standard error stream to a file using &>. This is useful when you

don’t want to send any output to the screen and instead save

everything in a log file (perhaps for later analysis).

ls -l / &> stdout_and_stderr.txt

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Redirecting standard output and standard error streams to a file

To append both the standard output and standard error streams to

a file, simply use double chevron (&>>).

What if we wanted to send the standard output stream to one file,

and the standard error stream to another? This is also possible using

the streams’ file descriptor numbers:

$ ls -l / 1> stdout.txt 2> stderr.txt

Listing 1-12

Redirecting standard output and standard error to separate files

Black Hat Bash (Early Access) © 2023 by Dolev Farhi and Nick Aleks