bash script to check whether a username exists

Question

I followed the following thread How to create a bash script in Linux that checks if the user is local or not

I want to check number of arguments number received before checking the username

username=$1                                                                     
                                                                                
id -u $username > /dev/null 2>&1                                                
                                                                                
if [ $# -gt 0 ]; then                                                           
 if [ $? -eq 0 ]; then                                                          
  echo "$username exists"                                                       
  else                                                                          
  echo "$username doesn't exist"                                                
  fi                                                                            
else                                                                            
echo "num of arg are less than expected"                                        
fi

the script doesn't work properly, it always writes that the user exists

$? contains exit status of the most recently executed command. `[` is a command, too. — Cyrus, Dec 18 '22 at 08:27
See [Why is testing "$?" to see if a command succeeded or not, an anti-pattern?](https://stackoverflow.com/q/36313216/4154375). — pjh, Dec 19 '22 at 00:27
[Shellcheck](https://www.shellcheck.net/) reports several issues with the code. — pjh, Dec 19 '22 at 00:30

Gilles Quénot · Accepted Answer · 2022-12-18T09:16:40.297

As explained by Cyrus in comments, you are trying to test $? at the wrong place, because the test or [ command set $? too.

Better use this:

if getent passwd "$username" &>/dev/null; then
    echo 'user exists'
else
    echo 'user NOT exists'
fi

The getent password <username>, if not match a user, exit with a return code >= 1.
It's boolean logic. No need to test $?.

The same logic appears with id:

id nonexistant || echo "not exists"

bash script to check whether a username exists

1 Answers1