How can I redirect and append both stdout and stderr to a file with Bash?

Question

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

cmd > file.txt

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

cmd >> file.txt

To redirect both stdout and stderr to a truncated file, I know to use:

cmd &> file.txt

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

Answer 1

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.

Answer 2

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 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, 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 here: http://bash-hackers.org/wiki/doku.php/syntax/redirection#appending_redirected_output_and_error_output

Answer 3

In Bash you can also explicitly specify your redirects to different files:

cmd >log.out 2>log_error.out

Appending would be:

cmd >>log.out 2>>log_error.out

Answer 4

In Bash 4 (as well as ZSH 4.3.11):

cmd &>>outfile

just out of box

Answer 5

This should work fine:

your_command 2>&1 | tee -a file.txt

It will store all logs in file.txt as well as dump them on terminal.

Answer 6

Try this

You_command 1>output.log  2>&1

Your usage of &>x.file does work in bash4. sorry for that : (

Here comes some additional tips.

0, 1, 2...9 are file descriptors in bash.

0 stands for stdin, 1 stands for stdout, 2 stands for stderror. 3~9 is spare for any other temporary usage.

Any file descriptor can be redirected to other file descriptor or file by using operator > or >>(append).

Usage: <file_descriptor> > <filename | &file_descriptor>

Please reference to http://www.tldp.org/LDP/abs/html/io-redirection.html

Answer 7

I am surprised that in almost ten years, no one has posted this approach yet:

If using older versions of bash where &>> isn't available, you also can do:

(cmd 2>&1) >> file.txt

This spawns a subshell, so it's less efficient than the traditional approach of cmd >> file.txt 2>&1, but this approach feels more natural and understandable to me:

1. Redirect stderr to stdout.
2. Redirect the new stdout by appending to a file.

Also, the parentheses remove any ambiguity of order, especially if you want to pipe stdout and stderr to another command instead.