Bash script, find the next closed (not in use) port from some port range. Post: 303036751

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Top Forums UNIX for Beginners Questions & Answers Bash script, find the next closed (not in use) port from some port range. Post 303036751 by drysdalk on Wednesday 10th of July 2019 10:56:17 AM

07-10-2019

Registered User

Hi,

In terms of your script itself as a solution to your problem, a change like this should work:

Code:

#!/bin/bash
IP=$1
first_port=$2
last_port=$3
function scanner

{
for ((port=$first_port; port<=$last_port; port++))
        do
                if ! (echo >/dev/tcp/$IP/$port)2>/dev/null
                then
                        echo $port
                        return
                fi
        done
}

scanner

This will cause the first TCP port that cannot have a blank line written to it by the echo command to be echoed out to standard output. The key is the return statement, which will cause the function to end as soon as it is executed. So once we find the first port we can't write a blank line to, we print it out and return control to the next line of the script (which doesn't exist, and so the script ends at that point).

Now, a better question: what is it you actually need to do here, and why ? This script might well work for certain ports in certain circumstances, but a far better bet here would be to use a utility that is dedicated to the purpose of port scanning (like nmap, for example) rather than trying to re-invent the wheel with a shell script.

drysdalk

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list-jndi-resources

asadmin-list-jndi-resources(1AS)				   User Commands				  asadmin-list-jndi-resources(1AS)

NAME

       list-jndi-resources  - gets all the JNDI resources

SYNOPSIS

       list-jndi-resources --user admin_user [--password admin_password] [--host localhost] [--port 4848] [--secure |-s] [--passwordfile filename]
       [--terse=false]
	[--echo=false] [--interactive=true]

       Gets all the JNDI resources. This command is supported in remote mode only.

OPTIONS

       --user		       authorized domain application server administrative username.

       --password	       password to administer the domain application server.

       --host		       machine name where the domain application server is running.

       --port		       port number of the domain application server listening for administration requests.

       --secure 	       if true, uses SSL/TLS to communicate with the domain application server.

       --passwordfile	       file containing the domain application server password.

       --terse		       indicates that any output data must be very concise, typically avoiding human-friendly sentences and favoring well-
			       formatted data for consumption by a script.

       --echo		       setting to true will echo the command line statement on the standard output.

       --interactive	       prompts you for the required options that are not already specified.

       Example 1: Using the list-jndi-resource command

       asadmin> list-jndi-resource --user admin1
       --password adminadmin1 --host pigeon --port 5001
       Command list-jndi-resources executed successfully

EXIT STATUS

       0		       command executed successfully

       1		       error in executing the command

       asadmin-create-jndi-resource(1AS), asadmin-delete-jndi-resource(1AS)

J2EE 1.4 SDK							    March 2004					  asadmin-list-jndi-resources(1AS)