netstat in bash with proc

ns.sh

#! /bin/bash

#get all data
ROUTE=$(cat /proc/net/route | grep -v "Iface")
TCP=$(cat /proc/net/tcp | grep "[0-9]: ")
UDP=$(cat /proc/net/udp | grep "[0-9]: ")
SOCKETS=$(ls -l $(find /proc/*/fd/ -type l 2>/dev/null) 2>/dev/null | grep socket)


parse_ipv4()
{
    echo "$((16#${1:6:2})).$((16#${1:4:2})).$((16#${1:2:2})).$((16#${1:0:2}))"
}

parse_port()
{
    echo "$((16#$1))"
}

lookup_socket()
{
    inode=$1
    matches=$(echo "$SOCKETS" | grep "socket:\[$inode\]")
    pid=$(echo "$matches" | sed 's/.*\/proc\/\(.*\)\/fd\/.*/\1/')
    echo $pid
}

get_program()
{
    ps=$(ps --no-headers -f $1)
    a=($ps)
    program=${a[8]}
    echo $program
}

parse_line()
{
    status=${4}
    if [[ $status == "01" ]];
    then
        # only want listening
        return
    fi
    port=$(parse_port ${2:9:4})
    ip=$(parse_ipv4 ${2:0:8})
    uid=${8}
    inode=${10}
    pid=$(lookup_socket $inode)
    program=$(get_program $pid)
    printf "%15s:%-6s\t%-6s\t%-6s %s\n" $ip $port $uid $pid $program
}

parse_route()
{
    iface=$1
    gw=$(parse_ipv4 $3)
    dest=$(parse_ipv4 $2)
    mask=$(parse_ipv4 $8)
    printf "%10s\t%15s\t%15s/%-15s\n" $iface $gw $dest $mask
}

printf "%10s\t%15s\t%15s/%-15s\n" "Iface" "Gateway" "Destination" "Mask"
while read -r line;
do
    parse_route $line
done <<< "$ROUTE"

echo ""

printf "%15s:%-6s\t%-6s\t%-6s %s\n" "TCP IP" "PORT" "UID" "PID" "CMD"
while read -r line;
do
    parse_line $line
done <<< "$TCP"

echo ""

printf "%15s:%-6s\t%-6s\t%-6s %s\n" "UDP IP" "PORT" "UID" "PID" "CMD"
while read -r line;
do
    parse_line $line
done <<< "$UDP"

echo ""