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Old 11-11-2004, 12:52 AM   #1
blackzone
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shell short question(stdout, stderr)


I know:
command >/dev/null //output not shown
command 1>/dev/null //standard output not shown
command 2>/dev/null //standard error not shown
command 2&> /dev/null //standard output + error not shown

how about:
command 1>/dev/null 2>&1

it sends stdout to /dev/null and??
 
Old 11-11-2004, 02:47 AM   #2
Hko
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Quote:
how about:
command 1>/dev/null 2>&1

it sends stdout to /dev/null and??
...sends stdandard error (stderr) to the same place where standard input (stdin) is going.

Note that the order matters: "command 2>&1 >/dev/null" doesn't work because stderr is first redirected to the same place as stdout, after that, stdout is redirected to /dev/null.

In the case of redirecting to /dev/null it does not matter much which form you use, but when you want to redirect both stdout and stderr to a single file, this doesn't work: "command >my_file.txt 2>my_file.txt"
but this does: "command >my_file.txt 2>&1"

These forms are exactly the same, only the syntax is different:

command >some_file 2>&1
command 1>some_file 2>&1
command &> some_file
command >& some_file

And I suppose the one you mentioned ("command 2&> some_file") belongs to this list as well.
 
Old 11-11-2004, 03:12 AM   #3
perfect_circle
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Quote:
...sends stdandard error (stderr) to the same place where standard input (stdin) is going.
WRONG!!!
2>&1 redirects stderr to stdout, error messages get sent to the same place as standard output.

this is why
Code:
command 1>/dev/null 2>&1
is the same with
Code:
command &>/dev/null
.
Both redirect stderr and stdout to /dev/null
 
Old 11-11-2004, 07:39 AM   #4
jschiwal
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It redirects stderr to stdout which is redirected to /dev/null. The effect is the same as
2&>/dev/null.
 
Old 11-11-2004, 09:01 AM   #5
Hko
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Quote:
Originally posted by perfect_circle
WRONG!!!
2>&1 redirects stderr to stdout, error messages get sent to the same place as standard output.
TRUE,
I said by mistake: "standard input(stdin)", where it should have been: "standard output (stdout).

Thanks for correcting that.
 
  


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