Pololu USB AVR - Manual (Page 40)

avrdude -p m328p -c avrisp2 -P /dev/cu.usbmodem00022331 -U flash:w:test.hex
If all goes well, the output should look something like this:
avrdude: AVR device initialized and ready to accept instructions
Reading | ################################################## | 100% 0.01s
avrdude: Device signature = 0x1e950f
avrdude: NOTE: FLASH memory has been specified, an erase cycle will be performed
To disable this feature, specify the -D option.
avrdude: erasing chip
avrdude: reading input file "test.hex"
avrdude: input file test.hex auto detected as Intel Hex
avrdude: writing flash (3392 bytes):
Writing | ################################################## | 100% 0.88s
avrdude: 3392 bytes of flash written
avrdude: verifying flash memory against test.hex:
avrdude: load data flash data from input file test.hex:
avrdude: input file test.hex auto detected as Intel Hex
avrdude: input file test.hex contains 3392 bytes
avrdude: reading on-chip flash data:
Reading | ################################################## | 100% 0.72s
avrdude: verifying ...
avrdude: 3392 bytes of flash verified
avrdude: safemode: Fuses OK
avrdude done. Thank you.
Pololu USB AVR Programmer User's Guide © 2001–2014 Pololu Corporation
5. Getting Started in Mac OS X Page 40 of 54