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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 303036750 by yossi on Wednesday 10th of July 2019 10:36:31 AM
Old 07-10-2019
Bash script, find the next closed (not in use) port from some port range.

hi,
i would like to create a bash script that check which port in my Linux server are closed (not in use) from a specific range, port range (3000-3010).
the print output need to be only 1 port, and it will be nice if the output will be saved as a variable or in same file.

my code is:
Code:
#!/bin/bash
IP=$1
first_port=$2
last_port=$3
function scanner

{
for ((port=$first_port; port<=$last_port; port++))
        do
                (echo >/dev/tcp/$IP/$port)> /dev/null 2>&1 && echo $port open || echo "$port closed"
        done
}

scanner

than to run it i use:
./demo2.sh 127.0.0.1 3000 3010

the output for this code is:
Quote:
3000 open
3001 open
3002 closed
3003 closed
3004 closed
3005 closed
3006 closed
3007 closed
3008 closed
3009 closed
3010 closed
the result that i am trying to get is only:
Quote:
3002
 

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udp(n)								 Tnm Tcl Extension							    udp(n)

__________________________________________________________________________________________________________________________________________________

NAME
udp - Send and receive UDP datagrams. _________________________________________________________________ DESCRIPTION
The udp command allows to send and receive datagrams using the User Datagram Protocol (UDP) (RFC 768). UDP COMMAND
udp open [port] The udp open command opens a UDP datagram socket and returns an udp handle. The socket is bound to given port number or name. An unused port number is used if the port argument is missing. udp connect host port The udp connect command opens a UDP datagram socket and connects it to a port on a remote host. A connected UDP socket only allows to send messages to a single destination. This usually allows to shorten the code since there is no need to specify the destination address for each udp send command on a connected UDP socket. The command returns a udp handle. udp send handle [host port] message The udp send command sends a datagram containing message to the destination specified by host and port. The host and port arguments may not be used if the UDP handle is already connected to a transport endpoint. If the UDP handle is not connected, you must use these optional arguments to specify the destination of the datagram. udp receive handle The udp receive command receives a datagram from the UDP socket associated with handle. This command blocks until a datagram is ready to be received. In most cases, it might be a good idea to check for pending datagrams using the udp bind command. udp close handle The udp close command closes the UDP socket associated with handle. udp bind handle readable [script] udp bind handle writable [script] The udp bind command allows to bind scripts to a UDP handle. A script is evaluated once the UDP handle becomes either readable or writable, depending on the third argument of the udp bind command. The script currently bound to a UDP handle can be retrieved by calling the udp bind command without a script argument. Bindings are removed by binding an empty string. udp info [handle] The udp info command without the handle argument returns a list of all existing UDP handles. Information about the state of a UDP handle can be obtained by supplying a valid UDP handle. The result is a list containing the source IP address, the source port, the destination IP address and the destination port. SEE ALSO
scotty(1), Tnm(n), Tcl(n) AUTHORS
Juergen Schoenwaelder <schoenw@cs.utwente.nl> Tnm udp(n)
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