rtl_sdr:tldr:dc72a

The command "rtl_sdr" is used to control a software-defined radio (SDR) receiver using the Realtek RTL2832U chipset.

The "-f" flag is used to set the frequency of the receiver. In this case, the value "${100000000}" is a placeholder that likely needs to be replaced with an actual frequency value. The frequency is typically specified in Hz, so the example could be attempting to set the receiver to a frequency of 100,000,000 Hz (or 100 MHz).

The "-g" flag is used to set the receiver's gain. Again, the value "${20}" is a placeholder that should be replaced with an actual gain value. The gain determines the amplification of the incoming signal.

The "-" at the end of the command is common in Linux commands and typically indicates that the command should read input from the standard input stream (stdin). This is often used for piping or redirecting input/output in command-line operations, but without more context it's not clear how it's intended to be used here.