[SOLVED] How to redirect the error message?

Mike_Brown · 05-24-2015, 06:13 PM

I have a hostlist and there are several hosts. I want to use ssh to connect to them. I want to see whether the host is available or not by the time length of ssh takes. If it take long than 5s (which means it is not available). Then stop it, and ssh to next host. Once a host is available, then output the name of host. I previously use nmap, but the IT security told it is not allowed to install it on the desktop on campus.

Code:

    HOSTS=`cat $host_list`
    for line in $HOSTS
    do 
    ssh -o ConnectTimeout=5s $line true >> /dev/null
    RESULT=$?
    if [ $RESULT -eq 0 ]
    then
    echo $line > succeed.txt
    else
    echo $line > fail.txt
    fi
    done

The above script is all I can do.
The problem is when it is failed, I want to redirect the error message

Code:

ssh: connect to host c28-0112-05.ad.mtu.edu port 22: No route to host

. But I still get the error message.

Keith Hedger · 05-24-2015, 07:03 PM

>> means append to stream you want to use >, also > on its own redirects stdout, most apps send error to stderr which is stream 2 so you need to direct stderr to dev null with '2>/dev/null' to redirect both to /dev/null you can use 2>&1>/dev/null, wich redirects stderr to stdout and the directs stdout to dev/null, if you are using bash you can use &>/dev/null which does the same thing

Mike_Brown · 05-24-2015, 07:28 PM

Quote:

Originally Posted by Keith Hedger

>> means append to stream you want to use >, also > on its own redirects stdout, most apps send error to stderr which is stream 2 so you need to direct stderr to dev null with '2>/dev/null' to redirect both to /dev/null you can use 2>&1>/dev/null, wich redirects stderr to stdout and the directs stdout to dev/null, if you are using bash you can use &>/dev/null which does the same thing

I tried

Code:

[zwang10@c15-0331-04 ~/bin]$ ssh -o ConnectTimeout=5s c28-112a-05.ad.mtu.edu true 2 > & 1 > /dev/null
Ambiguous output redirect.

And

Code:

[zwang10@c15-0331-04 ~/bin]$ ssh -o ConnectTimeout=5s c28-112a-05.ad.mtu.edu true & > /dev/null
Invalid null command.

It does not work. I am using tcsh.

Ser Olmy · 05-24-2015, 07:35 PM

2 > is not the same as 2>. Same goes for & > vs. &>. Remove the spaces, and things should start working.

Keith Hedger · 05-25-2015, 05:50 AM

was offline but good catch with the spaces!