There are different possibilities:

1) ecprint -printer MyPrinter file.cgm | …

This will make ecprint read the configuration for MyPrinter as last used with EasyPlot or EasyCopy.
Setting are user specific and are saved in

$HOME/.easycopy/printers/MyPrinter on Linux

%USERPROFILE%\.easycopy\printers\MyPrinter on Windows.

Please be aware that in EasyCopy and EasyPlot, printer settings will automatically be saved when you use a printer.

2) ecprint @resfile file.cgm | …

This will make ecprint read settings from a so called “response file”.
You can create a response file based on an existing printer configuration by running: ecprint -printer MyPrinter -mkres resfile -help
The response file can be edited with a simple text editor to change options for ecprint.
You can use a combination of a response file and other options given on the commandline to override specific settings.

3) easyplot -print file.cgm -printer MyPrinter -nogui

This will print file.cgm on MyPrinter with the settings last used in EasyPlot.
If you do not give the -printer option it will print on the last used printer in EasyCopy or EasyPlot.
If you do not give the -nogui option it will bring up the print dialog and let you change settings.
Note, that ecprint only generates print data and need to be piped through lpr or whatever you are using (it could f.ex. be eclpd or ectcp) to send data to your printer, while EasyPlot knows what to do with the data given the printer configuration.