pgloader does this (and much much more) in a single command:

https://github.com/dimitri/pgloader

  pgloader \
    mysql://user:password@mysql:3306/database \
    postgresql://postgres:root@localhost:5432/postgres

This is a gem of a tool. Surprised nobody has mentioned it. Supports SQLite and MS-SQL too.

https://pgloader.readthedocs.io/en/latest/ref/mysql.html#