Q:

\copy table via psql from local to Docker container from within the container

Disclaimer: Not talking about this. 
How can I execute \copy command from psql when I'm inside the live docker container? 
When I try \copy table from '/home/Snow/Documents/table.csv' with delimiter as ',' csv header; 
I get the error:

No such file or directory

Is there a different path I should write? 

A:

From outside the container you can import a file using psql with the following command:
$ cat table.csv | psql -h docker_container -d db -c \
"COPY table FROM STDIN WITH DELIMITER ',' CSV"

Replace docker_container with the IP or hostname of the container
In case your postgres isn't configured to accept external connections, change it in the postgres.conf file: e.g. listen_addresses = '*' to listen to all external connections.