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

Reference link: http://unix.stackexchange.com/questions/70963/difference-between-2-2-dev-null-dev-null-and-dev-null-21

 

up vote3down votefavorite

5

Just looking for the difference between

• 2>&-
• 2>/dev/null
• |&
• &>/dev/null
• >/dev/null 2>&1

and their portability with non-Bourne shells like tcsh, mksh, etc.

io-redirection tcsh file-descriptors bourne-shell

shareimprove this question

edited Apr 3 '13 at 8:37 lesmana 5,12532040

asked Apr 3 '13 at 1:25 Det 12315

Note that, while mksh supports &> for GNU bash compatibility, it’s strongly encouraged to not use this, as parsing it can break the semantics of existing POSIX scripts, and mksh disables that in POSIX mode already. –  mirabilos Feb 27 at 13:56

add comment

2 Answers

activeoldestvotes

up vote6down voteaccepted

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) First let's tackle the function of these. For reference see the Advanced Bash-Scripting Guide. 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>/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. 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. &>/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. >/dev/null This is just an abbreviation for 1>/dev/null. It redirects file 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.