[ILUG] shell quiz !

[Conor Daly]

On Fri, Feb 16, 2001 at 03:32:10PM +0000 or thereabouts, Padraig Brady wrote:
> How about after each counterx=$((counterx+1)):
> if [ $counterx -gt 255 ] then break;
> ?
> 
> Also should the 2nd last line be counter1 and
> not counter 4?
> 
> Padraig.
> 
> John P . Looney wrote:
> 
> >  Here's a little puzzler. Seeing as "seq" only works in decimals, it's a
> > little tricky.
> > 
2 problems to deal with here:
> >  Basically, if someone gives me a pair of IP's, like
> > 
> >     10.55.2.9
> > and 
> >     10.10.29.2
> > 
> >  I want something like a "for $ip in $ips" type loop. I'm thinking at the
> > moment, something like:
> > 
> > IP_start=10.10.2.9
> > IP_end=10.10.6.0
1. You need to wrap from .9 to .0 via .255
2. IP=10.10.3.2 will never get scanned using IP_start=9
> > 
> > for i in `seq 1 4`
> > do
> >     eval "IP_start_$i=`echo $IP_start | cut -f$i -d. `"
> >     eval "IP_end_$i=`echo $IP_end | cut -f$i -d. `"
# Fix for ##--1--## below
if [ $IP_start_$i -gt $IP_end_$i ]; then
IP_end_$i=`expr $IP_end_$i + 255`
> > done
> > 
> >  counter1=$IP_start_1
> >  while [ $counter1 -le $IP_end_1 ] ; do
> >    counter2=$IP_start_2
> >    while [ $counter2 -le $IP_end_2 ] ; do
> >      counter3=$IP_start_3
> >      while [ $counter3 -le $IP_end_3 ] ; do
> >        counter4=$IP_start_4
> >        while [ $counter4 -le $IP_end_4 ] ; do
##--1--##
# This will fall over for the example above since $IP_start_4 is always
# greater than $IP_end_4
# The fix starts above at assignment time and continues with Padraig's
if [ $counterx -gt 255 ] then break;
# a fix for ##--2--## is a bit harder.  I'd rewrite the loop bigtime for
# this.  Fix attempt below. 
> >          echo "$counter1.$counter2.$counter3.$counter4"
> >          counter4=$((counter4+1))
> >        done
> >        counter3=$((counter3+1))
> >      done
> >      counter2=$((counter2+1))
> >    done
> >    counter4=$((counter4+1))
> >  done
> > 
> >  But, how do I do the "base 256" thing ?
##--2--##
# let's look at counter3 and counter4

# first, we need to take IP_start and IP_end out of the comparisons.  They
# can be replaced with $start4 and $end4 etc.  
# if counter3=IP-start_3 then we start with counter4=IP-start_4, otherwise we
# need to start with counter4=0.  if counter3=ip_end_3 then we finish with
# counter4=IP_end_4, otherwise we finish with counter4=255.  Now, its
# easy...

while [ $counter3 -le $end3 ] ; do
# if counter3 is at the beginning of its range, then counter4 need start
# only from the IP_start_4 point, otherwise it must start from zero
  if [ $counter3 -eq $IP_start_3 ]; then
    start4=$IP_start_4
  else 
    start4=0
  fi
# similarly, if counter3 is at the beginning of its range, then counter4 may
# end at the IP_end_4 point, otherwise it must go up to 255.
  if [ $counter3 -eq $IP_end_3 ]; then
# because IP_end_4 could be greater than 255 (see ##--1--## above), we need
# to take account of that when choosing the end point.  The same may be the
# case for IP_end_3 so the condition above may need work also.  I'm kinda
# thinking the IP_end_$i + 255 thing above may not be necessary using this
# kind of loop but I'll leave that as an exercise for the reader (or I can't
# be bothered figuring it out!-)
    if [ $IP_end_4 -gt 255 ];then
      end4=`expr $IP_end_4 - 255`
    else
      end4=$IP_end_4
    fi
  else
    end4=255
  fi
# I'm not sure if "start4" is required at all or if you could just use
# "counter4" in the initialisation above
  counter4=$start4
  while [ $counter4 -le $end4 ] ; do
    counter4=$((counter4+1))
  done
  counter3=$((counter3+1))
done

If we remove the "IP_end_$i + 255" from the script, the loop simplifies to 

while [ $counter3 -le $end3 ] ; do
  if [ $counter3 -eq $IP_start_3 ]; then
    counter4=$IP_start_4
  else 
    counter4=0
  fi
  if [ $counter3 -eq $IP_end_3 ]; then
    end4=$IP_end_4
  else
    end4=255
  fi
  while [ $counter4 -le $end4 ] ; do
    counter4=$((counter4+1))
  done
  counter3=$((counter3+1))
done

That's yer lot...


-- 
Conor Daly 
Met Eireann, Glasnevin Hill, Dublin 9, Ireland
Ph +353 1 8064217 Fax +353 1 8064275
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