inetd can make several programs with stdin input and stdout output work like programs with input and output from and to sockets, and monitor their listening sockets simultaneously.

Is there a simpler program than inetd which just works for a single program: make a single program with stdin input and stdout output work like a program with input and output from and to sockets?

Thanks.

Nmap’s Ncat can do this, with its -c or -e options:

nc -l -c bc

will listen on the default port (31337) and, when a connection is established, run bc with its standard input and output connected to the socket.

nc localhost 31337

will then connect to a “remote” bc and you can then enter bc expressions and see their result.

socat can do this too (thanks Hermann):

socat tcp-listen:31337,reuseaddr,fork EXEC:bc

There are plenty of UCSPI-TCP tools.

In the following, the server program is ./service, 0.0.0.0 or ::0 are the host IP addresses, and 7777 is the port number.

There are also (not listed in this answer but documented in the various tool collections, q.v.) UCSPI-UNIX and UCSPI-LOCAL tools for AF_LOCAL sockets, tools for doing the same with FIFOs, UCSPI-SSL tools for TLS/TCP sockets, and tools for Netlink sockets.

Bernstein ucspi-tcp

In Daniel J. Bernstein's ucspi-tcp, there is tcpserver:

tcpserver -v -P -R -H -l 0 0.0.0.0 7777 

./service

There are IPv6-capable enhanced versions of Bernstein ucspi-tcp such as Erwin Hoffman's tcpserver:

tcpserver -v -P -R -H -l 0 ::0 7777 

./service

Bercot s6-networking

Laurent Bercot's s6-networking has s6-tcpserver4:

s6-tcpserver4 -v 0.0.0.0 7777 

./service

s6-tcpserver6 -v ::0 7777 

./service

nosh UCSPI tools

The nosh toolset has tcp-socket-listen and tcp-socket-accept:

tcp-socket-listen --combine4and6 :: 7777 

tcp-socket-accept --verbose --localname 0 

./service

tcpserver -v -l 0 :: 7777 

./service

Pape ipsvd

Gerrit Pape's ipsvd has tcpsvd:

tcpsvd -v 0.0.0.0 7777 

./service

Sampson onenetd

Adam Sampson has a onenetd:

onenetd -v :: 7777 

./service

Further reading

• Protocol:
  
  
  
  
  • Jonathan de Boyne Pollard (2016). The gen on the UNIX Client-Server Program Interface. Frequently Given Answers.
  
  
  • Daniel J. Bernstein (1996). UNIX Client-Server Program Interface. cr.yp.to.
  
  
  
  


• toolsets:
  
  
  
  
  • Daniel J. Bernstein. ucspi-tcp. cr.yp.to.
  
  
  • 
    s6-networking. Laurent Bercot. skarnet.org.
  
  
  • Jonathan de Boyne Pollard (2018). nosh. Softwares.
  
  
  • Jonathan de Boyne Pollard (2018). djbwares. Softwares.
  
  
  • 
    ipsvd. Gerrit Pape. smarden.org.
  
  
  • 
    onenetd. Adam Sampson. offog.org.
  
  
  
  


• reference manuals:
  
  
  
  
  • Daniel J. Bernstein. The tcpserver program. ucspi-tcp.
  
  
  • Erwin Hoffmann. tcpserver. ucspi-tcp6. fehcom.de.
  
  
  • 
    s6-tcpserver4. Laurent Bercot. s6-networking. skarnet.org.
  
  
  • 
    s6-tcpserver6. Laurent Bercot. s6-networking. skarnet.org.
  
  
  • 
    tcpsvd. ipsvd. Gerrit Pape. smarden.org.
  
  
  • Jonathan de Boyne Pollard (2019). tcpserver. nosh Guide. Softwares.
  
  
  • Jonathan de Boyne Pollard (2019). tcp-socket-listen. nosh Guide. Softwares.
  
  
  • Jonathan de Boyne Pollard (2019). tcp-socket-accept. nosh Guide. Softwares.
  
  
  • Jonathan de Boyne Pollard (2019). tcpserver. djbwares. Softwares.
  
  
  
  

In addition to the programs listed by JdeBP, courier also uses a wrapper like this, called couriertcpd.