Bash Script Help

zokken · 03-25-2009, 12:39 PM

Hi,

I wrote a simple script to determine which of our users are forwarding their email and to what address, so that we can grab statistics about the usage of our mail system. The script works but I know it's not very efficient, so I'm just looking for some tips on how to improve it (which would also give me ideas for future scripts I write).

First let me explain a little bit about our mail system so the script makes sense.

- Non-system users are located in either /home/facstaff/ or /home/students/

- Each user is supposed to have a preferences file (though unfortunately, not everyone does), which stores the forwarding address (if there is one).

- If a user is forwarding, their preferences file contains the following line:

Code:

forward_addy=forwarding@address.com

- If a user is not forwarding, the same line should exist (although sometimes it doesn't) with no forwarding address. So:

Code:

forward_addy=

The script I wrote returns the username, whether they're facstaff or student, and either the forwarding address or 'none' if they're not forwarding. If anyone have any suggestions on how to improve it, let me know. I pasted it twice -- one without comments (in case that's easier to go through), and one with comments.

---

Code:

stdlist=`grep "home\/students" /etc/passwd | cut -f1 -d":"`
fslist=`grep "home\/facstaff" /etc/passwd | cut -f1 -d":"`
userlist=`echo $stdlist $fslist`

for i in $userlist; do
   echo -n "$i  "
   if grep "^$i" /etc/passwd | grep "home\/students" > /dev/null; then
      echo -n "student  "
   else
      echo -n "facstaff "
   fi
   if [ -f /usr/local/mail/$i.pref ]; then
      if grep forward_addy /usr/local/mail/$i.pref | grep -v "forward_addy=$" > /dev/null; then
         grep forward_addy /usr/local/mail/$i.pref | cut -f2 -d"="
      else
         echo none
      fi
   else
      echo none
   fi
done

---

Code:

# we want to eliminate all users who are not in /home/students/ or /home/facstaff/
# first we grab everyone in /home/students/
stdlist=`grep "home\/students" /etc/passwd | cut -f1 -d":"`

# next we grab everyone in /home/facstaff/
fslist=`grep "home\/facstaff" /etc/passwd | cut -f1 -d":"`

# now we add the two variables together to create a full list of users
userlist=`echo $stdlist $fslist`

# let's go through the entire list
for i in $userlist; do

# print the username
   echo -n "$i  "

# determine whether they're a student
   if grep "^$i" /etc/passwd | grep "home\/students" > /dev/null; then

# if so, state this
      echo -n "student  "

# otherwise, state that they're facstaff
   else
      echo -n "facstaff "
   fi

# make sure the user has a preferences file
   if [ -f /usr/local/mail/$i.pref ]; then

# if so, check if they're forwarding
      if grep forward_addy /usr/local/mail/$i.pref | grep -v "forward_addy=$" > /dev/null; then

# if they're forwarding, print the forwarding address
         grep forward_addy /usr/local/mail/$i.pref | cut -f2 -d"="

# if they're not forwrading, return 'none'
      else
         echo none
      fi

# if they don't have a preferences file, return 'none'
   else
      echo none
   fi
done

jan61 · 03-25-2009, 03:53 PM

Moin,

here's another idea (not fully tested, I don't have such a configuration):

Code:

getent passwd | cut -f1,6 -d: | sed -rn '/:\/home\/(student|facstaff)$/{s#:/home/# #;p}' | \
while read user group; do
  forward_addy=
  test -f /usr/local/mail/${user}.pref &&
    forward_addy=`sed -rn '/^forward_addy=/{s/.*=//;p}' /usr/local/mail/${user}.pref`
  test -z "$forward_addy" && forward_addy=none
  echo "$user $group $forward_addy"
done

Goals:
- I try to minimize external program calls within the loop
- I try to prepare the data outside the loop

How does it work?
- the getent reads all lines from the passwd file
- the cut leaves only the necessary fields (user name and home directory)
- this output (user:/path/to/home) is the input for the sed
- the sed uses extended regex (-r) and is quiet by default (-n)
- only lines matching ":/home/facstaff" or ":/home/student" are processed
- for matching lines: replace ":/home/" with a blank, print the result
- the result is "user student" or "user facstaff"
- now feed a read loop, within the loop I can use $user and $group
- default $forward_addy to empty string
- if the prefs file exists: use one sed to get the "forward_addy" line and remove all but the part after "="
- if $forward_addy is empty: set to "none"
- now output the result

So I reduce the external calls to 3 outside the loop and one within each loop.

Jan

zokken · 03-26-2009, 08:36 AM

Interesting, thanks for the reply. I need to improve my sed skills.