How to Check Which Shell You Are Using

Bash's man page mentions there's two ways to redirect stderr and stdout: &> file and >& file. Now, notice that it says both stderr and stdout.

In case of this >file 2>&1 we are doing redirection of stdout (1) to file, but then also telling stderr(2) to be redirected to the same place as stdout ! So the purpose may be the same, but the idea slightly different. In other words "John, go to school; Suzzie go where John goes".

What about preference ? &> is a bash thing. So if you're porting a script, that won't do it. But if you're 100% certain your script will be only working on system with bash - then there's no preference

Here's an example with dash , the Debian Amquist Shell which is Ubuntu's default.

$ grep "YOLO" * &> /dev/null
$ grep: Desktop: Is a directory
grep: Documents: Is a directory
grep: Downloads: Is a directory
grep: Music: Is a directory
grep: Pictures: Is a directory
grep: Public: Is a directory
grep: Templates: Is a directory
grep: Videos: Is a directory
grep: YOLO: Is a directory
grep: bin: Is a directory

As you can see, stderr is not being redirected

To address your edits in the question, you can use if statement to check $SHELL variable and change redirects accordingly

But for most cases > file 2>&1 should work

In more technical terms, the form [integer]>&word is called Duplicating Output File Descriptor, and is a feature specified by POSIX Shell Command Language standard, which is supported by most POSIX-compliant and Brourne-like shells.

See also What does & mean exactly in output redirection?

Most terminals (at least gnome-terminal, urxvt, and XTerm, for example) that are started within a desktop environment such as Unity will use the SHELL environment variable to select the shell when they are launched.

SHELL should automatically be set to your default shell listed in /etc/passwd, but the variable can be overwritten when you log in. Make sure you have not set SHELL=/bin/bash or something similar in a file that will affect your entire desktop session. Such files include:

• ~/.profile
• ~/.pam_environment
• /etc/environment
• maybe some other files edited by Ubuntu users less often, such as /etc/profile

Additionally if any scripts such as ~/.bashrc or ~/.bash_profile are called by those other startup files and there is an export SHELL=/bin/bash line, that will also affect the entire desktop session.

I know it's acceptable/encouraged, but I still hate answering my own question. Nevertheless, this may be of some use to someone in the future. Thanks to @heemayl and @muru for helping me investigate.