podman/docs/source/markdown/options/attach.md

--attach, -a=stdin | stdout | stderr

Attach to STDIN, STDOUT or STDERR.

In foreground mode (the default when -d is not specified), podman run can start the process in the container and attach the console to the process's standard input, output, and error. It can even pretend to be a TTY (this is what most command-line executables expect) and pass along signals. The -a option can be set for each of stdin, stdout, and stderr.