Is there any way, using basic Unix commands, to find the next unused port number, starting at port 4444 and going upwards? I'm ssh'ed (via openssh) into a Windows XP machine, running Cygwin tools and using a bash shell.
Thanks, - Dave
for port in $(seq 4444 65000); do echo -ne "\035" | telnet 127.0.0.1 $port > /dev/null 2>&1; [ $? -eq 1 ] && echo "unused $port" && break; done
seq 4444 65000 - port range for check echo -ne "\035" - escape character to force close telnet session (^])
if telnet finishes with exit code 1 that mean connection refused:
$ telnet 127.0.0.1 4444 Trying 127.0.0.1... telnet: connect to address 127.0.0.1: Connection refused telnet: Unable to connect to remote host $ echo $? 1
else we decided that connection was success with exit code 0.
Special for cygwin: You need to install additional package
inetutils that is contain telnet port and use the script as follows:
for port in $(seq 4444 65000); do echo -ne "\035" | /usr/bin/telnet 127.0.0.1 $port > /dev/null 2>&1; [ $? -eq 1 ] && echo "unused $port" && break; done