from:tldr:a5d57
from: List mail in the specified mailbox directory.
$ MAIL=${path-to-mailbox} from
try on your machine
This command is assigning the value of the variable MAIL to the variable path-to-mailbox.
The syntax MAIL=${path-to-mailbox} is known as variable assignment in shell scripting languages like Bash. It sets the value of the variable named MAIL to the value of the variable named path-to-mailbox.
The variable path-to-mailbox should be defined somewhere else in the script, and its value will be used to set the value of the MAIL variable.
This explanation was created by an AI. In most cases those are correct. But please always be careful and
never run a command you are not sure if it is safe.