Johannes Buchner

You got 2 Linux/Unix PCs across the country, and between them are two big firewalls and proxies.
So each one can basically only send HTTP-Requests to the Internet, not directly to each other.

Having a little php script on a webserver, I wrote 2 shell scripts so one can interact across this connection.

The script for the machine you want to control:

#!/bin/bash
# The client's script
SERVER="http://<fill in server adress>/exchange.php"
GETURL=$SERVER"?mode=get&what=commands"
TARGETURL=$SERVER"?mode=gather&what=output"
TMP=/tmp/O-zero.1
while sleep 3
do
wget --quiet --output-document - ${GETURL} |
sed 's/\r$//'
done |
bash 2>&1 3>&1 4>&1 5>&1 |
while sleep 1
do
# We don't want every line in a seperate request
# So we group them:
{
echo -n "a="
while read -t 2 line
do
echo "$line"
done
} > $TMP
# Send output if we have some
if [[ $(wc -c <$TMP) != "2" ]]; then
wget --quiet --post-file $TMP --output-document - $TARGETURL
fi
done

The script for the operator:

#!/bin/bash
# The operator's script
SERVER="http://<fill in server adress>/exchange.php"
GETURL=$SERVER"?mode=get&what=output"
TARGETURL=$SERVER"?mode=gather&what=commands"
TMP=/tmp/O-zero.2
while sleep 3
do
wget --quiet --output-document - ${GETURL} |
sed 's/\r$//'
done &
while read line;
do
echo "a=$line" > $TMP
wget --quiet --post-file $TMP --output-document - $TARGETURL
done
wait

The script on the Webserver (commands.txt and output.txt must be writeable).

<?php
header('Content-Type: text/plain');
if($_GET['what'] === 'commands')
$file = 'commands.txt';
if($_GET['what'] === 'output')
$file = 'output.txt';
if($_GET['mode'] === 'gather' && !empty($file)){
$fd = fopen($file,"a");
@fwrite($fd,$_POST['a']);
}
if($_GET['mode'] === 'get' && !empty($file)){
echo join(file($file));
$fd = fopen($file,"w");
}
?>