How to redirect and append both standard output and standard error to a file with Bash

To redirect standard output to a truncated file in Bash, I know to use:

cmd > file.txt

To redirect standard output in Bash, appending to a file, I know to use:

cmd >> file.txt

To redirect both standard output and standard error to a truncated file, I know to use:

cmd &> file.txt

How do I redirect both standard output and standard error appending to a file? cmd &>> file.txt did not work for me.

cmd >>file.txt 2>&1

Bash executes the redirects from left to right as follows:

1. >>file.txt: Open file.txt in append mode and redirect stdout there.
2. 2>&1: Redirect stderr to "where stdout is currently going". In this case, that is a file opened in append mode. In other words, the &1 reuses the file descriptor which stdout currently uses.

There are two ways to do this, depending on your Bash version.

The classic and portable (Bash pre-4) way is:

cmd >> outfile 2>&1

A nonportable way, starting with Bash 4 is

cmd &>> outfile

(analog to &> outfile)

For good coding style, you should

• decide if portability is a concern (then use the classic way)
• decide if portability even to Bash pre-4 is a concern (then use the classic way)
• no matter which syntax you use, don't change it within the same script (confusion!)

If your script already starts with #!/bin/sh (no matter if intended or not), then the Bash 4 solution, and in general any Bash-specific code, is not the way to go.

Also remember that Bash 4 &>> is just shorter syntax — it does not introduce any new functionality or anything like that.

The syntax is (beside other redirection syntax) described in the Bash hackers wiki.