Shell Programming and Scripting

#!/usr/bin/awk -f
{
        for (offset = c =0; i = index(substr($0, offset + 1), "s"); offset += i){
                c++;
                if ((c == 1) || (c == 5))
                        print "Occurence " c " @ " offset + i;
        }
        if ((c != 1) && (c != 5))
                print "Last occurence @ " offset + i
}

[mute@geek ~]$ echo mississippis | ./offset
Occurence 1 @ 3
Occurence 5 @ 12
[mute@geek ~]$ echo mississippi | ./offset
Occurence 1 @ 3
Last occurence @ 7

echo 'M2011-07-0603:53:23M0ISETM' | fold -w1 |  egrep -n 'M'