Shell Programming and Scripting

S=${1:6}
IP="Logged this from host ${S%:*}"
P=${S##*:}
if [ "$P" = "*" ]
then # case B
    echo "$IP"
elif I=$(expr index $P '-')
then # case D
    echo "$IP range ${P:0:$((I-1))} ${P:$I}"
elif I=$(expr index $P ',')
then # case C
    echo -e "$IP port ${P:0:$((I-1))}\n$IP port ${P:$I}"
else # case A
    echo "$IP port $P"
fi

S=${1:6}	                            <-- initializing S as an array / what is 1:6?
IP="Logged this from host ${S%:*}"    <-- implies take any value before :
P=${S##*:}	                            <-- implies take any value after :
if [ "$P" = "*" ]	                            <-- check if value of P is eq to *
then # case B
    echo "$IP"
elif I=$(expr index $P '-')	            <-- locates the char '-' in P and returns index value (?) to I (why?) / how is I = 3 here?
then # case D
    echo "$IP range ${P:0:$((I-1))} ${P:$I}"	<-- $(P:0:2) is 100 (how?) / $(P:3) is port 110
elif I=$(expr index $P ',')	           <-- checks if there is a (,) in P
then # case C
    echo -e "$IP port ${P:0:$((I-1))}\n$IP port ${P:$I}" <-- same check as above
else # case A
    echo "$IP port $P"
fi

$ cat logfile
tcp://1.2.3.4:80
tcp://1.2.3.4:*
tcp://1.2.3.4:80,8080
tcp://1.2.3.4:80-101

$ awk -F ":|/" '/\*$/ {printf "Logged this from host %s\n",$4;next}
              /,/ {split($5,a,",") ; for (i in a) printf "Logged this from host %s port %s\n", $4, a[i];next}
              /-/ {sub(/-/," ",$5) ; printf "Logged this from host %s range %s\n",$4,$5;next}
              {printf "Logged this from host %s port %s\n",$4,$5}' logfile

Logged this from host 1.2.3.4 port 80
Logged this from host 1.2.3.4
Logged this from host 1.2.3.4 port 80
Logged this from host 1.2.3.4 port 8080
Logged this from host 1.2.3.4 range 80 101

while read L
do
# Put the above code here but modify the first line
# S=${1:6}
S=${L:6}
# (... remaining of the code)
done < logfile

#!/bin/bash
Split() {    # Function to make an array with a variable
    eval "$1=( \"$(echo "${!1}" | sed "s/$2/\" \"/g")\" )"
}
while read L
do
    Split L ':' # Makes an array ( 0:Protocol 1:IP 2:Port(s) )
    if [ ${L[0]} = tcp ]
    then
        IP="Logged this from host ${L[1]:2}" # :2 to remove the 2 slashes from host IP
        P=${L[2]}
        Split P ',' # makes an array with port numbers
        if [ "$P" = "*" ]    # case B
        then echo "$IP"
        elif I=$(expr index $P '-') # case D
        then    echo "$IP range ${P:0:$((I-1))} ${P:$I}"
        else # case A & C
            for ((i=0; i<${#P[@]}; i++))
            do
                echo "$IP port ${P[$i]}"
            done
        fi
    else
        echo "Other protocol : ${L[0]}"
    fi
done < infile