#!/bin/bash# dev-tcp.sh: /dev/tcp redirection to check Internet connection.# Script by Troy Engel.# Used with permission. TCP_HOST=www.dns-diy.com   # A known spam-friendly ISP.TCP_PORT=80                # Port 80 is http.  # Try to connect. (Somewhat similar to a 'ping' . . .) echo "HEAD / HTTP/1.0" >/dev/tcp/${TCP_HOST}/${TCP_PORT}MYEXIT=$?: <<EXPLANATIONIf bash was compiled with --enable-net-redirections, it has the capability ofusing a special character device for both TCP and UDP redirections. Theseredirections are used identically as STDIN/STDOUT/STDERR. The device entriesare 30,36 for /dev/tcp:  mknod /dev/tcp c 30 36>From the bash reference:/dev/tcp/host/port    If host is a valid hostname or Internet address, and port is an integerport number or service name, Bash attempts to open a TCP connection to thecorresponding socket.EXPLANATION   if [ "X$MYEXIT" = "X0" ]; then  echo "Connection successful. Exit code: $MYEXIT"else  echo "Connection unsuccessful. Exit code: $MYEXIT"fiexit $MYEXIT