Check Whether a User Exists

问题:

I want to create a script to check whether a user exists. I am using the logic below:

# getent passwd test > /dev/null 2&>1 # echo $? 0 # getent passwd test1 > /dev/null 2&>1 # echo $? 2

So if the user exists, then we have success, else the user does not exist. I have put above command in the bash script as below:

#!/bin/bash  getent passwd $1 > /dev/null 2&>1  if [ $? -eq 0 ]; then     echo "yes the user exists" else     echo "No, the user does not exist" fi

Now, my script always says that the user exists no matter what:

# sh passwd.sh test yes the user exists # sh passwd.sh test1 yes the user exists # sh passwd.sh test2 yes the user exists

Why does the above condition always evaluate to be TRUE and say that the user exists?

Where am I going wrong?

UPDATE:

After reading all the responses, I found the problem in my script. The problem was the way I was redirecting getent output. So I removed all the redirection stuff and made the getent line look like this:

getent passwd $user  > /dev/null

Now my script is working fine.

回答1:

you can also check user by id command.

id -u name gives you the id of that user. if the user doesn't exist, you got command return value ($?)1

回答2:

Why don't you simply use

grep -c '^username:' /etc/passwd

It will return 1 (since a user has max. 1 entry) if the user exists and 0 if it doesn't.

回答3:

There's no need to check the exit code explicitly. Try

if getent passwd $1 > /dev/null 2>&1; then     echo "yes the user exists" else     echo "No, the user does not exist" fi

If that doesn't work, there is something wrong with your getent, or you have more users defined than you think.

回答4:

This what I ended up doing in a Freeswitch bash startup script:

# Check if user exists if ! id -u $FS_USER > /dev/null 2>&1; then     echo "The user does not exist; execute below commands to crate and try again:"     echo "  root@sh1:~# adduser --home /usr/local/freeswitch/ --shell /bin/false --no-create-home --ingroup daemon --disabled-password --disabled-login $FS_USER"     echo "  ..."     echo "  root@sh1:~# chown freeswitch:daemon /usr/local/freeswitch/ -R"     exit 1 fi

回答5:

I suggest to use id command as it tests valid user existence wrt passwd file entry which is not necessary means the same:

if [ `id -u $USER_TO_CHECK 2>/dev/null || echo -1` -ge 0 ]; then  echo FOUND fi

Note: 0 is root uid.

回答6:

Actually I cannot reproduce the problem. The script as written in the question works fine, except for the case where $1 is empty.

However, there is a problem in the script related to redirection of stderr. Although the two forms &> and >& exist, in your case you want to use >&. You already redirected stdout, that's why the form &> does not work. You can easily verify it this way:

getent /etc/passwd username >/dev/null 2&>1 ls

You will see a file named 1 in the current directory. You want to use 2>&1 instead, or use this:

getent /etc/passwd username &>/dev/null

This also redirects stdout and stderr to /dev/null.

Warning Redirecting stderr to /dev/null might not be such a good idea. When things go wrong, you will have no clue why.

回答7:

I was using it in that way:

if [ $(getent passwd $user) ] ; then         echo user $user exists     else         echo user $user doesn\'t exists     fi

回答8:

Login to the server. grep "username" /etc/passwd This will display the user details if present.

回答9:

Late answer but finger also shows more information on user

  sudo apt-get finger    finger "$username"

回答10:

Depending on your shell implementation (e.g. Busybox vs. grown-up) the [ operator might start a process, changing $?.

Try

getent passwd $1 > /dev/null 2&>1 RES=$?  if [ $RES -eq 0 ]; then     echo "yes the user exists" else     echo "No, the user does not exist" fi

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