Perform text-processing task on remote server using shell variable specified on local machine

Question

I'm trying to write a shell script that proceses user information on a remote server via SSH. The user to be processed will be read interactively by the script.

• My current attempt looks like this

  #!/bin/bash echo "Enter username which u want to add" read Student3 ssh root@serverIP "useradd $Student3;" awk -F: '{print $1, $3, $6, $7}' /etc/passwd | grep "^${Student3}" 

  and it creates empty output.

• Without the grep call, the output is

  root 0 /root /bin/bash bin 1 /bin /sbin/nologin daemon 2 /sbin /sbin/nologin adm 3 /var/adm /sbin/nologin lp 4 /var/spool/lpd /sbin/nologin sync 5 /sbin /bin/sync shutdown 6 /sbin /sbin/shutdown halt 7 /sbin /sbin/halt mail 8 /var/spool/mail /sbin/nologin operator 11 /root /sbin/nologin 

• With the grep call appended as | grep "^${Student3}", I get empty output.

Answer 1

You are expecting the user that you added to show up in the local /etc/passwd. If it's the file on the remote system that you want to parse with awk, then you need to use ssh to access the data:

#!/bin/bash read -r -p 'Username: ' user # Add user and check the remote /etc/passwd file ssh remote "useradd '$user' && cat /etc/passwd" | awk -F : -v user="$user" '$1 == user { print $1, $3, $6, $7 }' 

That last pipeline could also be written

ssh remote "useradd '$user' && getent passwd '$user'" | awk -F : '{ print $1, $3, $6, $7 }' 

Note that you unlikely want to parse the /etc/passwd data with a regular expression like ^$user as this would match any user with a username that starts with whatever string in $user. The two variations of code above avoid this by not using a regular expression match and instead doing string comparisons of the complete username.