/dev/null not working as expected

[Sujoy Choudhury]

Hi,

I have a statement like this:

COMMAND="which java" RUN_COMMAND=`eval "$COMMAND"` > /dev/null echo "Output of the command:"$RUN_COMMAND

Here if java doesn't exist in the system it throws some output like
no java in (/usr/local/bin:/usr/bin
And I don't want this to be on the console.
So, even after redirecting the output to /dev/null it's still sending the output to the console.
Any idea?

[Koen Aerts]

Try something like:

COMMAND="which java 2> /dev/null"
RUN_COMMAND=`${COMMAND}`

[Sujoy Choudhury]

Thanks a lot Koen!
Well I modified to my need so that I don't have to write that in every command.

COMMAND="which java"  
RUN_COMMAND=`eval "$COMMAND"" 2> /dev/null"`   
echo "Output of the command:"$RUN_COMMAND 

This worked nicely.

[Tim Holloway]

Sujoy Choudhury wrote:
So, even after redirecting the output to /dev/null it's still sending the output to the console.

Unix (Linux) doesn't have a "the output". It has 2 outputs: stdout and stderr. The constructs ">xxxx" and "1>xxxx" redirect stdout to "xxxx", but do not affect stderr. The construct "2>xxxx> redirects stderr to "xxxx" but does not affect stdout. The construct ">& xxxx" redirects both stdout and stderr to "xxxx".

Your problem was that the output was being channelled to stderr when you thought it would be going to stdout.

[Sujoy Choudhury]

Thanks a lot Tim!
Nice explanation...