Shell: Difference in Output Forwarding

To remind the magic behind: 2>&-, 2>/dev/null, |&, &>/dev/null and >/dev/null 2>&1...

I/O Redirection Theory

For background:

• a number 1 = standard out (i.e. stdout)
• a number 2 = standard error (i.e. stderr)

If a number is not explicitly given, then number 1 is assumed by bash (shell).

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Functions

2>&-

The general form of this one is M>&-, where M is a file descriptor number. It closes output for whichever file descriptor is referenced, i.e. M.

2>/dev/null

The general form of this one is M>/dev/null, where M is a file descriptor number. It redirects the file descriptor, M, to /dev/null.

2>&1

The general form of this one is M>&N, where M and N are file descriptor numbers. It combines the output of file descriptors M and N into a single stream.

|&

This is just an abbreviation for 2>&1 |, which was added in Bash 4.

&>/dev/null

This is just an abbreviation for >/dev/null 2>&1, which redirects the file descriptor 2 (stderr) and the descriptor 1 (stdout) to /dev/null.

>/dev/null

This is just an abbreviation for 1>/dev/null, which redirects the file descriptor 1 (stdout) to /dev/null.

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Reference and Study Materials

For further details, please see the Advanced Bash-Scripting Guide and stackexchange.com.