Support a placeholder substitution like [bed_temperature_[current_extruder]]

[jamagin]

While filing #4308 I realized it would be useful if slic3r supported a placeholder such as [bed_temperature_[current_extruder]] when using multiple extruder printers. This way it would be possible to configure the starting g-code to preheat the bed to the temperature of the first filament that you are using.

Admittedly with a dual-extrusion print with vastly different temperatures it still might be necessary to manually override this.

[lordofhyphens]

There is a way to do what you want right now: conditional gcode. #3390

Put a separate {if ...} block in for each extruder your printer supports and Slic3r will omit the lines that evaluate to false (or 0).

[Maxwellfire]

The conditional execution works, but there doesn't seem to be a placeholder for multiple bed temperatures.

This means that bed_temperature_0 is not resolved as a placeholder, and what mmagin wanted doesn't work with conditional gcode either.