bash: redirect and append both stdout and stderr

Question

To redirect stdout in bash, overwriting file

cmd > file.txt

To redirect stdout in bash, appending to file

cmd >> file.txt

To redirect both stdout and stderr, overwriting

cmd &> file.txt

How do I redirect both stdout and stderr appending to file? cmd &>> file.txt does not work for me

Answer 1

cmd >>file.txt 2>&1

Answer 2

There are 2 ways, 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 classic way)
• decide if portability even to Bash pre-4 is a concern (then use classic way)
• no matter which syntax you use, not 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, in general any Bash specific code, is not the way to go.

Also remember that Bash 4 &>> is just shorter writing, it does not introduce any new functionality or similar.

Syntax is (beside other redirection syntax) described here: http://bash-hackers.org/wiki/doku.php/syntax/redirection#appending_redirected_output_and_error_output