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Old 02-18-2009, 03:35 AM   #1
crispyleif
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Bash for beginners @ TLDP.ORG, chapter 8, question


According to the guide:

ls -l * 2> /var/tmp/unaccessible-in-spool
will redirect standard output of the ls command to the file unaccessible-in-spool in /var/tmp.

I can't get that to be correct, if I issue such a command I get an empty file and standard output on the screen. Ideas ?
 
Old 02-18-2009, 03:52 AM   #2
ebmi
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`command 2> file` means that stderr will be redirected to "file"

`command 1> file` is for redirecting stdout to "file"

Cheers.
 
Old 02-18-2009, 04:14 AM   #3
colucix
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Yes. There is no message sent to the standard error. When you use redirection to a file, the file is created when the command execution starts, so that it can rest unused if no error message comes out from the execution. If you want to redirect the standard output together with the standard error you can do this:
Code:
ls -l * > /var/tmp/unaccessible-in-spool 2>&1
that is you redirect the standard output to the file, then the standard error to the same place as the standard output. The order of redirections is important!

You can also try a different command to see the standard error file populated by an error message:
Code:
ls -l pippo 2> /var/tmp/unaccessible-in-spool
provided you do not have a file named "pippo" in your current directory.
 
Old 02-18-2009, 04:25 AM   #4
ebmi
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Bash also supports

`command &> file`

for redirecting both stdout and stderr into "file". Other shells (such as dash) may or may not support this.
 
Old 02-18-2009, 04:58 AM   #5
crispyleif
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Thanks for all help.

I actually agree 100% with my result and with you.

when a command that produces no errer redirects that non-existent
errer to a file, I expect it to be empty.

What confused me was that the guide said that "2>" would redirect stdout,
which it doesn't.
 
Old 02-18-2009, 06:17 AM   #6
chrism01
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Must be a typo in the guide. It happens... sometimes you can't trust the book...
 
  


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