I won't invent anything new here but I'll share a quick improvement on an answer I've found on Stack Overflow.

If you are doing batch actions and don't want to write in .mylogin.cnf file, there's the trick: use a process substitution!

$ mysqldump --defaults-extra-file=<(printf "[client]\nhost = host.rds.amazonaws.com\nuser = username\npassword = \$PassW0rd\$") \
    database > dump.sql

This also works for any other file input, like Docker env file run param:

What is the fastest way to inject #envvars into a #Docker container?

docker run --env-file <(env) alpine env

The previous command will mirror your host env in an Alpine container. Now, it’s so easy to inject only some var:

docker run --env-file <(env | grep "AWS_") alpine env

— Joris Berthelot (@JorisBerthelot) January 21, 2021

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Joris Berthelot