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Im writing a bash-script to perform an offsite backup, using rsync over SSH. I'm able to send STDOUT to logger, for logs via
rsync --del -az -e 'ssh -i mycrt.crt' /home/gnutt/backup/ me@offisite:backup | logger -i
But I want to send STDERR instead, so if there is a problem, such as that offsite is unavailable, that output should be sent to logger and logged.
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Understanding the concept of redirections and file descriptors is very important when working on the command line. To redirect stderr and stdout , use the 2>&1 or &> constructs.
The regular output is sent to Standard Out (STDOUT) and the error messages are sent to Standard Error (STDERR). When you redirect console output using the > symbol, you are only redirecting STDOUT. In order to redirect STDERR, you have to specify 2> for the redirection symbol.
stdout − It stands for standard output, and is used to text output of any command you type in the terminal, and then that output is stored in the stdout stream. stderr − It stands for standard error. It is invoked whenever a command faces an error, then that error message gets stored in this data stream.
You can redirect the STDERR descriptor (2) to STDOUT (1) by adding 2>&1, for example:
rsync --del -az -e 'ssh -i mycrt.crt' /home/gnutt/backup/ me@offisite:backup 2>&1 | logger -i
If you want stderr instead of stdout (rather than stderr AND stdout), you can do the following:
Which looks like this:
rsync --del -az -e 'ssh -i mycrt.crt' /home/gnutt/backup/ me@offisite:backup 9> /dev/null 1>&9 2>&1 | logger -i
Alternately, you could employ process substitution:
logger -i <( rsync --del -az -e 'ssh -i mycrt.crt' /home/gnutt/backup/ me@offisite:backup > /dev/null )
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