@baja615
Initial post lists all possible commands.

Modern MTP devices with RWFS write to the card with path "2:/" (in that case "1" is for the hidden RWFS partition of the device), older MSM-only devices such as nuvi 2, 5 & 7 series, 1xx0, 2xx0 etc. use "1" for the card. Curiously, even earlier devices nuvi 3x0/6x0 have the card's path as "2" like the much later MTP devices.

The most commonly used commands are "rrgn" to copy a region's contents to card and "xrgn" to write the contents of a BIN file from the card to a region. Less commonly used is "ergn" which permanently erases a region's contents so must be used very carefully. Other commonly used and handy commands are "copy" and "del" to write or delete specific files and "copydir" to dump a directory/folder, eg. "0:/.System", "0:/Garmin" etc. or just "0:/" for the entire file system usually visible in MSM and in that familiar form. The latter can also be done by dumping rgn48 or rgn83 depending on if older or newer device, such a dumped file system BIN file can be opened (with 7-Zip or PowerISO for example) to yield individual files and folders either for examination, modification for flashing back, or to decide on its possible deletion. Alterations/deletions can be done manually and the folder/files recompiled into a BIN file using an advanced program such as PowerISO (but not 7-Zip, it's only for extraction). That BIN file can be flashed back using rrgn command. Note that using ergn on 48/83 will then require the file system to be properly formatted to FAT32 using RMPrepUSB or similar software.

A command will only work if it's written in the device's firmware by Garmin. None of the old 'region-only' devices without a visible file system have any commands in their fw, e.g. StreetPilot 2xxx, 3xx. Some modern device fw may lack certain commands, e.g. nuvi 13xx/14xx don't have "if_error" and some Asian versions of common US/EU devices may lack some commands. To check their presence open a firmware BIN or RGN file (don't use a GCD as that can be unreliable) and, for example, search for r.r.g.n in a hex reader where "." is a wildcard character. Some regions are protected against copying/writing. Some regions are encrypted ... NV regions 41 or 154 for example usually show only all "FF" content but that's because the hex reader cannot interpret the encrypted content.

Ldr.bin is simply the boot.bin (the ramloader) renamed. Because there's no 'fail-safe' check matching the device's HWID against that of the fw's 'safe-naming' as done with Updater.exe flashing of XXXX01000xxx.RGN (where XXXX is the firmware's HWID), this method can be dangerous if the incorrect Ldr.bin is used in the correctly named HWID folder for the device because it only checks the folder's name, not the actual HWID in the Ldr.bin file itself. Flashing foreign data to the device's virtual region 12 (0x0C) which in-turn writes to physical regions 5 & 43 on next boot attempt. As rgn5 is the bootloader the device may then be permanently hard-bricked which is why it's better that anyone who doesn't fully understand the process does not make these kits or alter any existing kits. A lot of dead units have resulted from early experimentation when we were learning how to safely use these commands.

Note that after a card has been used correctly, in the HWID folder along with Ldr.bin & update.txt there should now also be created the files named "last_id.bin" and "update.log". Some devices require an empty "update.log" file to be present for any cmd to be successfully initiated (e.g. some early devices like nuvi 2xx i think). The file "last_id.bin" is created after a flash and it must be removed before the card can be used again to flash the same or identical device.