The reason is you have a simple syntactic error, but lets first go over what you have done correctly, because there are some good points.

First, you have found a fundamental structure in Unix: you can use the return code of a program to determine how it has operated. In this case you - correctly - try to use the return code of "cmp". Very good.

Second, you have found out another fundamental thing: like in the C programming language throughout Unix a value of 0 is considered to be a logical TRUE while every other value is considered to mean a logical FALSE.

Now to your error: the correct syntax of the if-statement is:

Code:

if [ :TRUE: ] ; then
     some_commands
else
     some_other_commands
fi

Consider ":TRUE:" to be some process (or set of processes in a pipeline) or condition which either results in a "0" (TRUE) or another integer (FALSE).

In the historical Unix there was a command called "[", which was a link to the command "/usr/bin/test", which is still there. I suggest you read to man page of "test" to find out which possibilities it has. Basically "test" gets some logical expression and like any other program returns "0" (if the logical expression results in TRUE) or "1" (FALSE).

Because "[" was a normal program (most shells have implemented it as an internal command in the meantime, but Unix is adamant about being backwards compatible) it is clear why before and after it there have to be spaces: the rest of the line up to "]" are commandline arguments to "test" and therefore there have to be spaces like "ls-l" is wrong and "ls -l" is right.

Try the following two scripts:

Code:

#!/bin/ksh
if 0 ; then
     echo TRUE
else
     echo FALSE
fi

#!/bin/ksh
if [ 1 = 1 ] ; then
     echo TRUE
else
     echo FALSE
fi

In the first script then change the "0" to "1" or another integer and try again - notice what happens in the light of what i did say.

In the second script change the (obviously true) expression to another expression and experiment. Watch the output.

Bonus question: the expression "1 = 1" is working, but in fact the expression is not suited for comparing integer values ("=" is for comparing strings). How should it be phrased as true integer comparison? Hint: consult the man page!

You should now be able to change your script to work. That leaves two questions:

1) You now feed some file content to the while-loop, but this is hardly an up-to-date user directory. It is a good development device, though, so i am very satisfied that you had this idea to "simulate having this list" for the moment. It is a clever way of solving one problem after the other - i do exactly the same when writing scripts. Still, you have to solve the problem of "how to obtain a list of all defined users in a machine" and - "how to get the subset of this list i am interested in"? Any ideas?

2) Notice, that you output only "$path" to an output file, and not, what you want to stand there. If you prepare the output file this way it will be intermediary in nature and this is not, what you want. Is there a way to manipulate strings in the shell and - if this is possible - which commands might be useful for this purpose? Hint: consult your classes written material, the recommended book or whatever you got in this class rather than the "man-page" first - this is something the man-pages are poorly suited to research. Once you have a good idea of string-manipulating commands read their man pages of course.

All in all I'm quite satisfied with your progress so far - you might not know it but you are close to the solution. Keep up the good work.

I hope this helps.

bakunin