Shell script - remote execution on multiple servers

for sys in systemname1 systemname2 systemname3 systemname4 systemname5 
do
     ssh ${sys} do_command
done

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or with systemnames from a file:

for sys in $( cat systemnamefile )
do
     ssh ${sys} do_command
done

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If your commands will take a long time to run, you can use one of the many parallel ssh wrappers or...

Just append an & to the end of do_command above.

If working from an X workplace, try clusterssh to run one command on many systems.

is below statement will work?

for sys in systemname1 systemname2 systemname3 systemname4 systemname5
do
     ssh ${sys}  "rpm -qa | grep httpd"
done

The syntax looks fine and when I run something similar, it works as expected. Please don't award me any points. They should be given to noci as it is their answer.

for sys in systemname1 systemname2 systemname3 systemname4 systemname5 
do
     ssh ${sys}  bash -c  "rpm -qa | grep httpd"
done

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definitely will work as expected. (the | will need to be executed on the remte system ==>  it needs to be expanded on a command line on the remote system.
bash -c will do just that.

Having tested your original, noci, using the quotes works for me on my distro as well, without explicitly using bash.

@martyn, openssh does that, but not all ssh = openssh.  I do know of one that doesn't do /bin/sh -c...  (openvms)

Also the default shell of the user is taken from the password file if that is a menu or /bin/false there will be problems anyway.

@noci, thanks for the clarification. I imagined that there was a good reason for mentioning it specifically.

dssh handles it quite nicely

@noci, whatever menu or shell configured on the remote system is bypasssed when you pass a command to run. which is why setting /bin/false as the shell for user that should not be able to login does not work.

passing arguments white spaces or complex commands to ssh tend to be a total pain in pretty much all cases

if those are needed, you may resort to the easier

ssh destination sh -s <<EOF
set "$@"
# shell commands here
EOF