Remote Command executed via ssh does not return proper return code. Return error code is always "0", even condition failed

Question

I am not getting proper exit return code during execution of remote script on a Linux machine. This script is intended for checking whether a user exists or not.

My Script is below :-

#!/bin/bash DATE=`date "+%d-%m-%Y_%H:%M:%S"` for i in `cat /home/sandeep/server_ip_list/serverlist_New` do ipaddress=${i} echo -e "\n***************" >> /tmp/userfind_${DATE}.txt echo -e "$ipaddress" >> /tmp/userfind_${DATE}.txt for b in `cat /home/sandeep/Project_finduser01/userslist` do userid=${b} echo -e "\n" >> /tmp/userfind_${DATE}.txt echo -n "$userid" >> /tmp/userfind_${DATE}.txt ssh -t sandeep@${ipaddress} "grep $userid /etc/passwd > /dev/null; if [ "$?" = "0" ]; then echo -n " : User exsits" else echo -n " : User not exsits" fi" >> /tmp/userfind_${DATE}.txt done done 

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I am always getting the output below, whether the user exists or not:

*************** 10.25.59.12 sandeepj: User exsits pravin: User exsits ram: User exsits sita: User exsits raj.singh: User exsits 

How to manipulate remote exit status codes at server side?

Answer 1

The main issue in your code is that $? is expanded before ssh is called. This is due to quoting. All expansions in a double-quoted string are expanded before the string is used. In addition to that, the double-quoted string that you are using with ssh contains other double-quoted sections. These sections would be unquoted, just like the substring abc is unquoted in "123"abc"456".

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Instead of trying to execute a complicated command on the remote host, just let the ssh command cat the passwd file, then grep that:

if ssh -n "sandeep@$ipaddress" cat /etc/passwd | grep -q -F -e "$userid" then echo "User exists" else echo "User does not exist" fi >>"/tmp/userfind_$DATE.txt" 

Also, consider reading from the user and server list using a while loop instead:

while IFS= read -r userid; do # ... done </home/sandeep/Project_finduser01/userslist 

You may also redirect the outermost loop to your output file instead of redirecting every single echo:

while ...; do while ...; do # stuff done <userlist done <serverlist >"/tmp/userfind_$DATE.txt" 

If your user list is long, you may want to only get the passwd from the remote host once, and then query that several times

while ...; do scp "sandeep@$ipaddress:/etc/passwd" passwd.tmp while ...; do if grep -q -F -e "$userid" passwd.tmp; then # exists fi done <userlist done <serverlist >"/tmp/userfind_$DATE.txt" 

Even more efficiently would be to read the user list into an awk array and then match the usernames from the passwd file against them. That would get rid of the innermost loop entirely.

The username is found in a particular field in the passwd file. With your approach, you would match both marc and marco if you searched for marc. To match a bit more carefully, consider using a pattern such as "^$userid:" instead of matching against the whole line (and drop the -F that I introduced above if you're still using grep to do this).

You may also avoid the parsing of the passwd file completely with

getent passwd "$userid" >/dev/null 

This returns a zero exit code (success) if the user exists and non-zero otherwise.

I.e.,

if ssh -n "sandeep@$ipaddress" getent passwd "$userid" >/dev/null then # exists else # does not exist fi 

This would do one ssh call against the remote host per user though. This could be made a bit more efficient by not closing the connection between each call (the below would keep the connection open for one minute):

if ssh -n -o ControlMaster=auto -o ControlPersist=1m "sandeep@$ipaddress" getent passwd "$userid" >/dev/null then # exists else # does not exist fi 

Answer 2

Why not capture the result code from $? like so…

ssh user@host 'cmd arg;echo $?'

If you assign that to a variable you can then use a [ $n -gt 0 ] test against it.

Answer 3

After applied suggested changes if find two ways to achieve my result.

First Solution : Using for Loop

#!/bin/bash/expect DATE=`date "+%d-%m-%Y_%H-%M-%S"` for i in `cat /root/project_finduser/serverlist`; do echo -e "\n*******************" echo -e "$i" for a in `cat /root/project_finduser/userslist`; do echo -e "\n" echo -n "$a :" if ssh "root@${i}" cat /etc/passwd | grep -w -q -F -e "$a"; then echo "User exsits" else echo "User not exsits" fi done done >>"/tmp/userfind_${DATE}.txt" 

Second Solution : Using While loop { I have passed -n option with ssh command becuase while loop stop reading argument from file after first line}

 #!/bin/bash DATE=`date "+%d-%m-%Y_%H-%M-%S"` while IFS= read -r ipaddress; do echo -e "\n*******************" echo -e "$ipaddress" while IFS= read -r userid; do echo -e "\n" echo -n "$userid : " if ssh -n "root@${ipaddress}" getent passwd "$userid" >/dev/null; then echo -n "User exsits" else echo -n "User not exsits" fi done < /root/project_finduser/userslist done < /root/project_finduser/serverlist >"/tmp/userfind_${DATE}.txt" 

Output :

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192.168.56.103

sandeep : User exsits

student : User exsits

ram : User not exsits

sita : User not exsits

swati : User exsits

student : User exsits

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192.168.56.104

sandeep : User not exsits

student : User exsits

ram : User not exsits

sita : User not exsits

swati : User not exsits

student : User exsits