Like this?
socat tcp-listen:8080,reuseaddr,fork system:'ls; exec socat - tcp\:localhost\:80'
1st parameter gets ,fork to have socat stay listening for more connections
system: is preferred over exec: to have a shell interpreter and easily run an additional command after the ls command,
which is a new socat command
which will have stdin/stdout connected to the remote client's output/input and will forward it bidirectionally again to the next destination. Note that its : separator (and a few other special characters) must be escaped with a \ to not confuse the first socat command. If this line becomes more complex it become easier to simply exec a script like this:
socat tcp-listen:8080,reuseaddr,fork exec:/path/to/myscript.sh
with /path/to/myscript.sh:
#!/bin/sh
ls
exec socat - tcp:localhost:80
exec in the shell command is optional but avoids uselessly leaving around the shell.
socat also exports a few variables of its own that can be reused in the script, that you could check for example like this (with a connection made):
$ env - socat TCP-LISTEN:8080,reuseaddr,fork exec:printenv
SOCAT_PID=1057351
SOCAT_PPID=1057284
SOCAT_VERSION=1.7.4.1
SOCAT_SOCKADDR=127.0.0.1
SOCAT_SOCKPORT=8080
SOCAT_PEERADDR=127.0.0.1
SOCAT_PEERPORT=42970
