Connection testing with Perl
Since I'm seldom in control of all the devices between myself and whatever system I am trying to reach, I often like to verify whether I will be able to connect to a particular port on the particular system before I concern myself with whether my connection is behaving as it should. For example, I can use a command such as "telnet remhost 9999" and then try to determine if the response I am getting is the one I was expecting. If I have appropriate access to both systems, however, I can start a process on the particular port I want to reach and then run a test to see whether I can reach that process from the other system.
A little expertise with socket I/O can come in very handy for this kind of testing. You can get by, however, with a short but handy sample Perl script like one that I have used for many such tests over the years. I call my script, derived from many Perl command examples that I've encountered on the web, "listen". Listen will open any (non-busy) port above 1023 for a normal user and any (non-busy) port for root. It requires the Socket module for the muscle work and for definitions of most of the variables used (e.g., SOCK_STREAM).
The port that you want to open must be passed as an argument or the script will complain and immediately exit.
To test a port, you would type "./listen 9999" or something like that on one system and "telnet localhost 9999" on the same server or "telnet remhost 9999" (replacing "remhost" with the actual host name of the target system) on a remote server.
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nc
Nice script, but i find myself using netcat for this kind of thing:remote machine: 'nc -lp 9999'
local machine: 'telent remote 9999'
you should see a connection establish and then you will be able to type into the session and whatever you type will appear on the remote netcat session. you could also pipe a file into nc and it will be echoed in your telnet session:
'nc -lp 999 < /etc/motd'
This works on any machine with netcat installed (which I think should be default)
I hope this will be useful to you at some point sandra.
Especially useful on Solaris and the like
Yes, nc or netcat is a powerful utility which can do the same and much more and will be my first choice on Linux systems. However, nc is not available by default on Solaris and if you have constraints which prevent you from installing nc (for example, some crazy company policy), then this script is very handy. Thanks Sandra.