SSH in batch mode and File-Handles in a loop

Shell Programming and Scripting
1

Hi all
I try to execute SSH commands on several hosts in a while-loop.

There seems to be a problem with file-handle, first cycle works correct but no other one will follow due to the while condition is false even that there are many more host entries (lines) in all_hosts.dat.

#!/usr/bin/ksh
exec 0<all_hosts.dat
while read line
do
echo "...executing on host :" $line
ssh $line 'ls -la /tmp' # execution aborts after the first cycle
###pwd | ssh $line 'ls -la /tmp' # continues for each entry of all_hosts.dat
done # <all_hosts.dat
#

Any clue?
Any pointer to explaining tutorials about file handles?

MTIA

Dave

2

I too get the same error,ie the SSH session is entered once, in case of while loop.

But it doesnot seems to happen if i use for inplace of while

for host in $(</tmp/hosts); do
echo "Executing on the $host"
ssh $host 'ls -lrt /tmp'
echo $host
done

cat /tmp/hosts
user1@localhost
remote@localhost
others@localhost

Gurus,
Help us why did the code as in OP using the while doesnot work,but using the for loop is works?

Thanks
Nagarajan Ganesan

3

The problem is that ssh is reading from stdin.

Either have the loop reading from another file descriptor or redirect the stdin of ssh from somewhere else, e.g. /dev/null

4

... and

ssh -n 'command ...'

as written in the man page was the solution.

tks Chris