On Wed, Feb 01, 2012 at 07:03:33PM -0800, Peter Blajev wrote:
On Wed, Feb 1, 2012 at 2:53 PM, Stephen Harris lists@spuddy.org wrote:
On Wed, Feb 01, 2012 at 01:07:31PM -0800, Peter Blajev wrote:
echo " server2 server2" | \ while read confLine; do echo "--> $confLine" ssh peter@$confLine ls echo "--> END $confLine" done
Any idea what would cause the ssh command to break the while loop?
"ssh" is reading from stdin and passing the data over to the remote machine. You can test this with ssh peter@$confLine 'read x ; echo we got $x'
To stop it doing this, use the "-n" flag ssh -n peter@$confLine ls
Unfortunately I can't always use the (-n) option. If I wan't to send data through the pipe then the (-n) won't work. For example (on top of my head): mysqldump dB | ssh peter@remoteServer "mysql dB"
In this situation, ssh will read from the pipe and not from the "echo" statement and so it won't break your while loop.
The thing you need to understand is how redirection works. echo foo | while read do ... done
Everything from the "while" to the "done" will have stdin configured to read from the pipe (the output of "echo"). Here's an example: % echo "a b c d" | while read a do echo We have $a read b echo And $b done We have a And b We have c And d
You can see that the "read" statement inside the loop is reading from the pipe and so draining input.
An "ssh" on its own, in this situation, would drain _all_ the input. The "-n" flag tells ssh to not do this. But, equally, when you do sqldump | ssh then you've told ssh to take input from the output of sqldump, and so it's no longer reading the from outer loop.
Instead of "ssh -n" you could do "ssh < /dev/null" or "echo | ssh" or other options, and get the same sort of effect; you're setting up the stdin to ssh to be from somewhere _other_ than your main echo.