SSH Remote command exit code

Question

I know there are lots of discussions about it but i need you help with ssh remote command exit codes. I have that code: (scan is a script which scans for viruses in the given file)

for i in $FILES 
do
    RET_CODE=$(ssh $SSH_OPT $HOST "scan $i; echo $?")
    if [ $? -eq 0 ]; then
        SOME_CODE

The scan works and it returns either 0 or (1 for errors) or 2 if a virus is found. But somehow my return code is always 0. Even, if i scan a virus.

Here is set -x output:

++ ssh -i /home/USER/.ssh/id host 'scan Downloads/eicar.com; echo 0'
+ RET_CODE='File Downloads/eicar.com: VIRUS: Virus found.
    code of the Eicar-Test-Signature virus
0'

Here is the Output if i run those commands on the "remote" machine without ssh:

[user@ws ~]$ scan eicar.com; echo $?
File eicar.com: VIRUS: Virus found.
    code of the Eicar-Test-Signature virus
2

I just want to have the return Code, i dont need all the other output of scan.

!UPDATE!

It seems like, echo is the problem.

Jon · Accepted Answer · 2018-10-01 15:55:42Z

4

The reason your ssh is always returning 0 is because the final echo command is always succeeding! If you want to get the return code from scan, either remove the echo or assign it to a variable and use exit. On my system:

$ ssh host 'false'
$ echo $?
1
$ ssh host 'false; echo $?'
1
$ echo $?
0
$ ssh host 'false; ret=$?; echo $ret; exit $ret'
1
$ echo $?
1

answered Oct 1, 2018 at 15:55

Jon

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4 Comments

el-teedee Over a year ago

At the second example, you mean 0 as return value?

Jon Over a year ago

Yes, 'false; echo $?' has an exit value of 0, because the value comes from the (successful) echo command. The echo'd value is 1, though, because that comes from the false command.

Nico Over a year ago

Okey, then i missunderstood my own script. Now the script stops after the executed code because there is a newline in the output i guess. Is it exit 0 too, if i pipe the output to /dev/null?

Jon Over a year ago

The exit value will not be affected if you redirect the output.

Toby Speight · Accepted Answer · 2018-10-02 09:41:04Z

ssh returns the exit status of the entire pipeline that it runs - in this case, that's the exit status of echo $?.

What you want to do is simply use the ssh result directly (since you say that you don't want any of the output):

for i in $FILES 
do
    if ssh $SSH_OPT $HOST "scan $i >/dev/lull 2>&1"
    then
        SOME_CODE

If you really feel you must print the return code, that you can do that without affecting the overall result by using an EXIT trap:

for i in $FILES 
do
    if ssh $SSH_OPT $HOST "trap 'echo \$?' EXIT; scan $i >/dev/lull 2>&1"
    then
        SOME_CODE

Demo:

$ ssh $host "trap 'echo \$?' EXIT; true"; echo $?
0
0
$ ssh $host "trap 'echo \$?' EXIT; false"; echo $?
1
1

BTW, I recommend you avoid uppercase variable names in your scripts - those are normally used for environment variables that change the behaviour of programs.

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