Shell Programming and Scripting

So, I have no formal higher education in programming at all and am self taught. I am now wondering what would be considered best practices? Like should I hard code a variable, then compare it to what I want to know or achieve, or should I just put the commands with in the brackets?

Example, a script I am writing now loops through /Users to get all local (synchronized) accounts and checks their group membership of the admin group. If they are a member of the admin group a receipt file gets placed on the machine, and the policy is logged as being ran on that machine. If the results return back nothing the script just exits. Then I can build a policy report of every machine in my enterprise that has local admin accounts and go from there.

I know how to code all of this, but I am not sure what would be considered, "best practice."

Like, should I just construct it like this: if [[ some command with a loop == 1 ]] or if [[ $variable == 1 ]] then hard code my variable in the script?

It works either way I suppose.

Thanks for taking the time to read this.

Tom

Several points: [[ and [ may not have precisely the same semantics in some shells. example ksh.
try

Code:

type [  
type [[

Comparisons with string values are [ "string" = "string" ], not ==.

anyway - don't hard code values, except perhaps something that will never change,
example: a status return code of zero always means 'ok', so it can never change.

Why do this? because you can put all of the control variables right at the top of the code, so you can change behavior just by editing a few closely located lines of code. The other reason is that you could miss a "1" somewhere during an edit, completely breaking your code.

A lot of code examples on the forums here do not follow that practice because adding extra variables confuses people just starting out in scripting.

Thanks for your reply, but still got a few questions...

According to this document, which I have used to teach myself shell programming, [[ and [ have different abilities in bash.

source: Test Constructs

I have also read that = is used for an integer comparison and == is used for a string comparison, but it also says that "=" and "==" are synonyms in that same document. So the double ='s is probably unneeded I take it, but still allowed?

I have been programming in shell for a while now and am just trying to clean up my bad habits, if any to become a more efficient coder. I ended up not hard coding the variable in either, and put the command in the comparison. The script works as I wrote it, but I am getting an odd exit status error when running it in the terminal.

Thanks again for your time.

Tom

Yes, BASH has many extensions on the standard shell. But you can't depend on those extensions anywhere else.

As for numerical and string equality being identical, well -- given the same number base and no leading zeroes or extraneous sign symbols, a string comparison is no different than a numerical comparison. I've tried various things to trip them up, things like comparing positive and negative zero... it always acts just like a string comparison whether its one or two equals.

OK, thanks for the input. My script simply checks the local account's membership by grep -c from directory services, and if it returns a 1 then it is in the admin group, if it returns a zero the user is not. Then I I just use if/then to install a dummy receipt in /Library/Receipts from a manual triggered policy. Then I can take that policy log, and have a full list of all assets in the enterprise that have local admin accounts in /Users.

I am using OS X 10.5.8 in case some of this sounds odd to anyone.

Thanks again for the comments. I am sure I will have tons of more questions for you guys.

-T

Note tha you can use grep without brackets (and need of -c):

Code:

if grep somestring somefile
then
    do something
else
    do something else
fi

for the if/then (without else) statement, you can :

Code:

grep somestring somefile && do something

if there are more than 1 command in the "do something", put it between curly brackets { ... }