Difference between 2>&-, 2>/dev/null, |&, &>/dev/null, >/dev/null, 2>&1

For background:

• a number 1 = standard out (i.e. STDOUT)
• a number 2 = standard error (i.e. STDERR)
• if a number isn't explicitly given, then number 1 is assumed by the shell (bash)

Functions

2>&-

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

2>&1

The general form of this one is M>&N, where "M" & "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. It was added in Bash 4.

2>/dev/null

The general form of this one is M>/dev/null, where "M" is a file descriptor number. This will redirect the file descriptor, "M", to /dev/null.

>/dev/null

This is just an abbreviation for 1>/dev/null. It redirects file descriptor 1 (STDOUT) to /dev/null.

&>/dev/null

This is just an abbreviation for 2>&1 >/dev/null. It too was added in Bash 4. It redirects file descriptor 2 (STDERR) and descriptor 1 (STDOUT) to /dev/null.

Portability to non-bash, tcsh, mksh, etc.

I've not dealt much with other shells outside of csh and tcsh. My experience with those 2 compared to bash's redirection operators, is that bash is superior in that regard. See the tcsh man page for more details.

Of the commands you asked about none are directly supported by csh/tcsh. You'd have to use different syntaxes to construct similar functions.