tcpclient(1) create an outgoing TCP connection


tcpclient [ -46hHrRdDqQv ] [ -ilocalip ] [ -plocalport ] [ -Ttimeoutconn ] [ -llocalname ] [ -ttimeoutinfo ] [ -Iinterface ] host port program [ arg ... ]


tcpclient attempts to connect to a TCP server. If it is successful, it runs program with the given arguments, with descriptor 6 reading from the network and descriptor 7 writing to the network.

The server's address is given by host and port. host may be 0, referring to the local machine, or a dotted-decimal IP address, or a host name; if a host has several IP addresses, tcpclient tries each in turn. port may be a numeric port number or a port name.

tcpclient sets up several environment variables, as described in tcp-environ(5).


Use localip as the IP address for the local side of the connection; quit if localip is not available.
Use localport as the port number for the local side of the connection; quit if localport is not available.
Use interface as the local network interface. This is only defined for IPv6 sockets and needed if you use link-local IPv6 addresses.
Give up on the connection attempt after timeoutconn seconds. Default: 60. This timeout applies to each IP address tried.
(Default.) Delay sending data for a fraction of a second whenever the remote host is responding slowly, to make better use of the network.
Never delay sending data; enable TCP_NODELAY. This is appropriate for interactive connections.
Quiet. Do not print any messages.
(Default.) Print error messages.
Verbose. Print all available messages.


(Default.) Look up the remote host name for TCPREMOTEHOST.
Do not look up the remote host name; unset TCPREMOTEHOST.
Do not look up the local host name; use localname for TCPLOCALHOST.
(Default.) Attempt to obtain TCPREMOTEINFO from the remote host.
Do not attempt to obtain TCPREMOTEINFO from the remote host.
Give up on the TCPREMOTEINFO connection attempt after timeoutinfo seconds. Default: 26.
Fall back to IPv4 sockets. This is necessary for terminally broken systems like OpenBSD which will not let IPv6 sockets connect to V4-mapped IPv6 addresses. Please note that this also applies to DNS lookups, so you will have to use an DNS resolver with an IPv6 address to connect to IPv6 systems. Use DNSCACHEIP to set the DNS resolver IP dynamically.
Force IPv6 mode in UCSPI environment variables, even for IPv4 connections. This will set $PROTO to TCP6 and put IPv4-mapped IPv6 addresses in TCPLOCALIP and TCPREMOTEIP.