Shell script to handle SSH return value

I tried below if block, but it enters only on success scenario. when exception its not even entering if block

ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem  ec2-user@${targetIP}
if [ "$?" != "0" ]; then
 ssh -o StrictHostKeyChecking=no -i ~/.ssh/secondkey.pem  ec2-user@${targetIP}
fi

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@enthuguy

I have written sample script at my system:
cat 29176838.sh

#/bin/bash
targetIP=123.456.78.910
USERNAME=root
ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem  $USERNAME@${targetIP} "pwd;if [ \"\$?\" != \"0\" ];
then
        echo \"Using: ssh -o StrictHostKeyChecking=no -i ~/.ssh/secondkey.pem  $USERNAME@${targetIP}\";
        ssh -o StrictHostKeyChecking=no -i ~/.ssh/secondkey.pem  $USERNAME@${targetIP} \"pwd\";
else
        echo else;
fi"
ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem  $USERNAME@${targetIP} "/usr/bin/pwd"

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a)
We need to use \" when we are using any quote.
Example1:

$ /usr/bin/ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem murugesandins@123.456.78.910 "pwd"
/home/murugesandins

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After using a command we can use \$? to validate if previous command executed successfully or not
Example1:

$ /usr/bin/ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem murugesandins@123.456.78.910 "ls -ld asd >/dev/null 2>&1;if [ 0 -ne \$? ];then echo asd file not found;fi"
asd file not found

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We have to use \$? when passing parameter to ssh
other wise $? from localhost will be passed to remote host.
Example3:

$ /usr/bin/ls -ld delete.txt
/usr/bin/ls: delete.txt: No such file or directory
$ /usr/bin/ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem murugesandins@123.456.78.910 "echo \"Value of => $? passed from localhost at remote host\""
Value of => 2 passed from localhost at remote host
$ /usr/bin/ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem murugesandins@123.456.78.910 "echo \"Value of => $? passed from localhost at remote host\""
Value of => 2 passed from localhost at remote host
$ /usr/bin/ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem murugesandins@123.456.78.910 "echo \"Value of => $? passed from localhost at remote host\""
Value of => 0 passed from localhost at remote host

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Value of => 2 passed from localhost at remote host
referring return value of $? due to delete.txt
Use \" when using doublt quotes from ssh

@enthuguy

Sample version0.1 script output:

$ cat ./29176838.sh
#/bin/bash
targetIP=123.456.78.910
USERNAME=root
#Change USERNAME as per your requirement
#Change targetIP as per your requirement
ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem  $USERNAME@${targetIP} "ls NotFound.txt >/dev/null 2>&1;if [ \"$?\" != \"0\" ];
then
        echo \"Using: ssh -o StrictHostKeyChecking=no -i ~/.ssh/secondkey.pem  $USERNAME@${targetIP}\";
        ssh -o StrictHostKeyChecking=no -i ~/.ssh/secondkey.pem  $USERNAME@${targetIP} \"pwd\";
else
        echo else;
fi"
ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem  $USERNAME@${targetIP} "pwd"
$ ./29176838.sh
else
/home/murugesandins/experts_exchange

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I updated that code again

$ cat ./29176838.sh
#/bin/bash
targetIP=123.456.78.910
USERNAME=root
#Change USERNAME as per your requirement
#Change targetIP as per your requirement
ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem  $USERNAME@${targetIP} "ls NotFound.txt >/dev/null 2>&1;if [ \"\$?\" != \"0\" ];
then
        echo \"Using: ssh -o StrictHostKeyChecking=no -i ~/.ssh/secondkey.pem  $USERNAME@${targetIP}\";
        ssh -o StrictHostKeyChecking=no -i ~/.ssh/secondkey.pem  $USERNAME@${targetIP} \"pwd\";
else
        echo else \$Ret;
fi"
$ ./29176838.sh
Using: ssh -o StrictHostKeyChecking=no -i ~/.ssh/secondkey.pem  root@123.456.78.910
/home/murugesandins/experts_exchange

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You code should work.

Try changing to this...

ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem  ec2-user@${targetIP}
res=$?
echo "# res: $res"
if [ "$res" != "0" ]; then
 ssh -o StrictHostKeyChecking=no -i ~/.ssh/secondkey.pem  ec2-user@${targetIP}
fi

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See what the actual value of $res might be. For failures, normally you'll see a non-zero error code.

Thanks so much murugesandins, that was very details. Really appreciate your time

Just wanted to provide the actual script syntax I execute. Do you think, I can still use dev/null. please help

ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem  ec2-user@${targetIP} 'bash -s' < ${scriptsHome}/dummy.sh "\"${var2}\" \"${var1}\" \"${type}\" \"${NasRemotePath}\" \"${var3}\""

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@enthuguy

Can you describe your requirement in detail?

I am not sure about your requirement:

#!/bin/bash
targetIP=123.456.78.910
USERNAME=murugesandins
ssh -o StrictHostKeyChecking=no -i ~/.ssh/firstkey.pem  ${USERNAME}@${targetIP} 'if [ -z "${scriptsHome}" ];\
then
	scriptsHome=/home/murugesandins
fi
if [ -f ${scriptsHome}/dummy.sh ]
then
	if [ -z "${var2}" ]
	then
		var2="hai2"
	fi
	if [ -z "${var1}" ]
	then
		var1="hai1"
	fi
	if [ -z "${var3}" ]
	then
		var3="hai3"
	fi
	if [ -z "${type}" ]
	then
		type="type"
	fi
	if [ -z "${NasRemotePath}" ]
	then
		NasRemotePath="NasRemotePath"
	fi
	echo "Output after executing following command:"
	echo ${scriptsHome}/dummy.sh "\"${var2}\" \"${var1}\" \"${type}\" \"${NasRemotePath}\" \"${var3}\""
	${scriptsHome}/dummy.sh "\"${var2}\" \"${var1}\" \"${type}\" \"${NasRemotePath}\" \"${var3}\""
fi'

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Sample output:

$ ./29176838_version2.sh
Output after executing following command:
/home/murugesandins/dummy.sh "hai2" "hai1" "type" "NasRemotePath" "hai3"
/home/murugesandins
"hai2" "hai1" "type" "NasRemotePath" "hai3"

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$ cat /home/murugesandins/dummy.sh
#!/bin/bash
pwd
echo $@

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Replace 123.456.78.910 murugesandins to required IP/username

Thank you and welcome.
Let us know if having further statement at current query ?

I think your problem may be that ssh is trying your first identity file, and if it fails, prompting for a password.

To avoid this, by forcing the use of the identity file, set the ChallengeResponseAuthentication and PasswordAuthentication options to no. I also do a trial run, by adding the "-n" option - this doesn't try to run a remote command, just connects and disconnects again. It allows me to work out which key worked, and to use that later to run the actual remote command you are trying to run. I report an error if neither key worked (also if the remote host was down).

VALID_KEY=""
ssh -n -o StrictHostKeyChecking=no -o ChallengeResponseAuthentication=no -o PasswordAuthentication=no -i ~/.ssh/firstkey.pem  ec2-user@${targetIP}
if [ $? -eq 0 ]; then
    VALID_KEY=firstkey.pem
else
    ssh -n -o StrictHostKeyChecking=no -o ChallengeResponseAuthentication=no -o PasswordAuthentication=no -i ~/.ssh/secondkey.pem  ec2-user@${targetIP}
    if [ $? -eq 0 ]; then
        VALID_KEY=secondkey.pem
    fi
fi
if [ ${VALID_KEY} ]; then
  # Here do the actual ssh command you want to use (where I have "remote_command")
  ssh -o StrictHostKeyChecking=no -i ~/.ssh/${VALID_KEY} ec2-user@${targetIP} remote_command
else
  echo "ERROR: No valid key found for host ${targetIP}" 1>&2
fi

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Couple of extra changes. I've used the mathematical test for the response ($? -eq 0) rather than the string test (!=) you used. We *know* that $? will be a number! Also the "1>&2" will redirect the standard output of the "echo" command to standard error.

Edit: Forgot the "-n" options on the two "test" ssh calls! There shouldn't be one on the last call, since that one *does* want to do work on the remote host.

One other thing. Is the original code you posted exactly as run? *Any* command (even an "echo") between the "ssh" and the "if" will overwrite the return code from the ssh. If you want to test a return code, the best thing is to store it in a variable in the line immediately after the command.

Thanks all

You're welcome!

Good luck!

$ echo wELcOME | /usr/bin/wc >/dev/null