远程命令替换失败

Question

What is missing here?

This works (proves the file is there):

[rundeck@den16 ~]$ ssh ${SSH_USER}@${BUILD_HOST} "cat ${WLS_E1DOMAIN_LOC}/nodemanager.process.id"
7504

This doesn't (says No such file or directory):

[rundeck@den16 ~]$ ssh ${SSH_USER}@${BUILD_HOST} "kill -9 `cat ${WLS_E1DOMAIN_LOC}/nodemanager.process.id`"
cat: /cygdrive/c/Oracle/Middleware/Oracle_Home/user_projects/domains/E1DevDomain/nodemanager/nodemanager.process.id: No such file or directory

kill: usage: kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill -l [sigspec]

Answer 1

As @kvantour said, the problem is that the command expansion is happening on the local computer. Another way to solve this is to use escapes to tell the local shell to pass through the characters that normally trigger command expansion:

ssh ${SSH_USER}@${BUILD_HOST} "kill -9 \`cat ${WLS_E1DOMAIN_LOC}/nodemanager.process.id\`"
                                       ^                                               ^

BTW, I also recommend using $( ) instead of backticks (and you only have to escape the $ , not the parentheses):

ssh ${SSH_USER}@${BUILD_HOST} "kill -9 \$(cat ${WLS_E1DOMAIN_LOC}/nodemanager.process.id)"
                                       ^

BTW^2, you can use echo on the command part of the ssh command to see what'll be sent to the remote computer. That is, it shows the command after the local shell has done its parsing, substitutions, etc, but before the remote shell has done its parsing etc. Like this:

$ WLS_E1DOMAIN_LOC=/some/path
$ echo "kill -9 \$(cat ${WLS_E1DOMAIN_LOC}/nodemanager.process.id)"
kill -9 $(cat /some/path/nodemanager.process.id)

Here, you can see that $WLS_E1DOMAIN_LOC did get substituted by the local shell, but the command substitution didn't.

(This is one of very few cases where echo ing a command is informative, rather than misleading.)

Answer 2

You are trying to pass a kill command to a server over ssh.

Unfortunately, all substitutions are done on the host side, and not the server side. The error you are getting from cat is an error which is generated on den16 and not BUILD_HOST . If you want to pass it to BUILD_HOST you have to use a pipe in this case. Normally you would use single quotes, but since you use shell variables already in there, you have to use a pipe

rundeck@den16 ~]$ ssh ${SSH_USER}@${BUILD_HOST} "cat ${WLS_E1DOMAIN_LOC}/nodemanager.process.id | xargs kill -9"