Shell Programming and Scripting

As many of you on this forum already know, I have asked quite a few questions already that were probably elementary compared to your knowledge of Unix, but I have been searching through countless web pages, and consulting various books on the subject, and I am making progress to an extent.
I'm trying to write a shell script, that has been giving me an extreme headache, and I have it pretty much figured out...except for one certain part...a loop. Let me show you what I have so far so you can get a better idea of what I am trying to accomplish.

echo -n ' Login ID?: '
read loginID
echo -n ' UID?: '

Here's where I need a loop that will check to see if the UID is unique or not by checking in /etc/passwd.
I have a some idea of how to implement grep in a while loop, but I'm not sure of where to put what.
I came up with an if statement that I think will work, but then that wouldn't loop.

read UID
if [ " `grep $UID /etc/passwd ` " = 0 ] ; then
echo -n ' UID already exists - please re-enter a new UID '
UID = $<

That's probably not syntactically correct, but I think I'm in the ballpark somewhere.

The next lines are simple enough for me...

echo -n ' GID?: '
read GID
echo -n 'Comment?: '
read comment
echo -n ' Home Directory?: '
read homeDir
echo -n ' Startup Program?: '
read strtProg

Next I would just add the useradd command, but I couldn't find the proper option for the Login ID, so I am writing it as a ? in the below command:

useradd -? $loginID -u $UID -g $GID -c $comment -d $homeDir -s $strtProg

Now, when the script is finished, I should have an entry in the file passwd.user like:

johnd:x:204:300:John Doe:/home/johnd:/bin/bash


Could someone please help me with this? I am extremely confused with all the examples I've been reading online with the seds and awks, gawks, etc.

Thank you kindly

Meanwhile, I guess I will go throw on another pot of coffee...looks like I won't be sleeping tonight.

You don't need to prompt for UID because useradd will default to the next available unique number. The login ID is mandatory and does not have an option letter - but it does have to be the last argument.

Here's an example of a loop...

Code:

UID=""
until [ -n "$UID" ] &&  grep -q ":$UID:" /etc/passwd
do
  printf "uid? "
  read UID
done

Relykk please put a useful discription as the subject of your threads.

we all assume you are here for help and assistance so there is no need to use that as your subject.

Sorry Optimus! I'll remember next time.

Ygor, I tried implementing the loop you showed to me, and two things are happening:

1) I keep getting prompted whether or not the UID is already existent, and


2) I'm getting an error on the UID = ""

Now, I do have some knowledge of programming. I did take a programming concepts course, but the syntax of this language is driving me crazy. I know that I need something like this:

Enter UID
read UID // Prime read?
while UID already exists OR until UID doesn't already exist
do
Please enter a different UID
read UID
end while

I'm just having one heck of a time with the proper syntax.

Now, I know that grep will search and return a value of 0 if it finds a match. So, I had tried to utilize this in a way of basing the loop on that information, but I'm obviously not piecing it together correctly.

Something like:

until grep $UID -ne 1
do
echo -n "UID in use - please re-enter"
read UID
end

I'm really getting discouraged. I've been playing around with this for the past few days, and my brain is pretty much fried at this point.

also remember you will get an error if loginID exceeds the max length for loginID.

Yes, but that isn't a problem at this point. Thanks though.

Whoops! I had made an error in my previous post. Try this instead....

Code:

UID=""
while [ -z "$UID" ] || grep -q ":$UID:" /etc/passwd
do
  printf "uid? "
  read UID
done

...note that in UID="" there are no spaces either side of the equals sign.

Another way would be to use a flag...

Code:

Flag="Loop"
while [ "$Flag" = "Loop" ]
do
  printf "uid? "
  read UID
  if [ -z "$UID" ]
  then
      echo "UID cannot be null"
  else
      if grep -q ":$UID:" /etc/passwd
      then
         echo "UID already exists"
      else
         echo "OK! UID is $UID"
         Flag="OK"
      fi
  fi
done