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One of the scripts I run over ssh was hanging and I found a solution for it on this site: http://www.snailbook.com/faq/background-jobs.auto.html
The site resolves the problem by adding this to the end of the command:
xterm < /dev/null >& /dev/null &
I think I know what part of it does, but can someone help explain?
The first part:
# For stdin, read from /dev/null
< /dev/null
The second part:
>& /dev/null
What does >& do? I've seen 2>&1 which is direct STDERR to STDOUT, but when there are no numbers, does that mean redirect everything to /dev/null?
976
/dev/null is a special filesystem object that discards everything written into it. Redirecting a stream into it means hiding your program's output. The 2>&1 part means "redirect the error stream into the output stream", so when you redirect the output stream, error stream gets redirected as well.
Usage of /dev/null It is mainly used to discard standard output and standard error from an output.
All write operations to /dev/zero succeed with no other effects. However, /dev/null is more commonly used for this purpose. When /dev/zero is memory-mapped, e.g., with mmap, to the virtual address space, it is equivalent to using anonymous memory; i.e. memory not connected to any file.
Think of /dev/null as a black hole. It is essentially the equivalent of a write-only file. Everything written to it disappears. Attempts to read or output from it result in nothing. All the same, /dev/null can be quite useful from both the command-line and in scripts.
Googling for 'stream redirection >& ' will let you find http://tldp.org/LDP/abs/html/io-redirection.html
which, among other things, tells you
>&j
# Redirects, by default, file descriptor 1 (stdout) to j.
# All stdout gets sent to file pointed to by j.
Maybe this already helps.
Or search the help of standard unix shells, like bash, for stream redirection.
Rgds,
Thomas
180
Yes, this means redirect both stdout and stderr to /dev/null.
From info "(bash)Redirections":
Redirecting Standard Output and Standard Error
Bash allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be redirected to the file whose name is the expansion of WORD with this construct.
There are two formats for redirecting standard output and standard error:
&>WORDand
>&WORDOf the two forms, the first is preferred. This is semantically equivalent to
>WORD 2>&1
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