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Permissions script

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# 1  
Old 01-10-2010
Permissions script
Hi there,

I've been having some frustrating problems with a permissions script. Basically I want it to to determine what permissions the owner, group and everybody has for the file passed in.
Here's what I've got:

Code:
#!bin/bash
echo -n "Enter filename: "
read file
owner=$( ls -l $file | cut -c 2,3,4 )
group=$( ls -l $file | cut -c 5,6,7 )
users=$( ls -l $file | cut -c 8,9,10 )
ownername=$( ls -l $file | cut -d " " -f 3 )

oread=NO
owrite=NO
oexec=NO
gread=NO
gwrite=NO
gexec=NO
uread=NO
uwrite=NO
uexec=NO

case $owner in
       *r*)    oread=YES ;;
       *w*)    owrite=YES ;;
       *x*)    oexec=YES ;;
esac

case $group in
        *r*)    gread=YES ;;
        *w*)    gwrite=YES ;;
        *x*)    gexec=YES ;;
esac

case $users in
        *r*)    uread=YES ;;
        *w*)    uwrite=YES ;;
        *x*)    uexec=YES ;;
esac
echo "                          READ    WRITE   EXECUTE" > perm
echo "OWNER $ownername  $oread  $owrite         $oexec" | tr '[a-z]' '[A-Z]' >> perm
echo "GROUP USERS               $gread  $gwrite         $gexec" >> perm
echo "EVERYBODY         $uread  $uwrite         $uexec" >> perm

It seems to display "YES" for all the permissions, even if this is not true. Any help would be appreciated
# 2  
Old 01-10-2010
Why did you chosen a case statement, it is wrong because, in a case statement only one case can be right.

So it means, if you have read permission, then you should not have write & execute. But this will not be the case at anytime.

Choose some other way, it is better.
# 3  
Old 01-10-2010
Ahh I see. I suppose another way would be to use loads of if statements then?
# 4  
Old 01-10-2010
I see why you're frustrated. I think you're thinking the case statement will continue to check each case even if it finds some that are true. Unfortunately there isn't a 'continue' command to allow this so when the first case it finds is true, it will break out.

What you will need to do it iterate through each permission and check if it is set or not. I've test this code out for you. Replace your 3 case statements with a for loop for each owner, group, and user set. Let me know how it goes.

Code:
for perm in r w x
do
  # Check if $perm is set, but we don't care to see the output
  echo $owner | grep ${perm} > /dev/null
  if [ $? -eq 0 ]   # if the result was true, then it is set
  then
    case $perm in
      r) oread=YES ;;
      w) owrite=YES ;;
      x) oexec=YES ;;
    esac
  fi
done

# 5  
Old 01-10-2010
Thank you very much, that works great now.
One more question, I don't quite understand why this line is used:
Code:
 echo $owner | grep ${perm} > /dev/null

Why are curly brackets used and why is the output directed to /dev/null ?
Last edited by user_invalid; 01-10-2010 at 09:52 AM..
# 6  
Old 01-10-2010
I have a habit of using curly braces around my variables to explicity state when the name of a variable starts and ends. Here's one example where it would be needed:

Code:
year=2010
month=01
echo ${year}_${month}   # echoes 2010_01
echo $year_$month   # echoes 01 because it looked for a variable called $year_ which I didn't define

Also without directing it to /dev/null, the output would show on the screen. Although your script would work, the end user doesn't really need to see this output. It was only done to test whether the permission was present, so we just needed "$?" that contained the success/failure code of that command.

Let me know if this helps or if you have any other questions.
# 7  
Old 01-17-2010
Sorry for the late reply. Thanks for all that it really helps and my bash scripting is coming along great now, learning so much everyday its a great feeling. I'm sure I'll be back at some point with more problems that frustrate me!
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