Use netcat to listen on a port and send output from a command when a client connects

I have a Raspberry Pi (Debian Linux) connected to my LAN that can read data from some connected devices and output it to STDOUT.

Let's say the program is run on "Server" and I want to serve the output of the script /usr/bin/data to port 1234.

I want any client to pull the output of that script by connecting to that port, using something like

nc Server 1234 > ServerData.txt

I want the server to stay alive, run the script for each connection, serve the data and then close the connection to the client. Server needs stay alive and wait for the next connection.

What is the netcat command to run on Server???

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1 Answer

One of the more advanced versions of netcat will be required. You can use ncat or socat:

Server Side

When client connects, execute the executable program /usr/bin/data and send program output to client.

NCAT Method:

$ ncat -l 1234 -c '/usr/bin/data' --keep-open

SOCAT Method

$ socat -U TCP-LISTEN:5403,fork EXEC:'/usr/bin/data',stderr,pty,echo=0

Client Side:

Connect to the server, and receive output from server.

NCAT Method to File

$ ncat Server 1234 | tee ServerData.txt

NC (netcat) Method to stdout

$ </dev/null nc <Server.ip> 5403 > /dev/stdout

to save to a file replace /dev/stdout with a file name

WGET Method to File

$ wget -q <Server.ip>:5403 -O myfile.txt

to print results replace myfile.txt with /dev/stdout

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