The DS3231 Real Time Clock (RTC), I2C address 0x68, will be used for the following examples:
The programs, i2cget and i2cset, both assume the I2C device has a single byte index register.
Thus, devices with no index register as well as those with two byte index registers don't work well with these tools.
Using i2cget, view indexed register 4 "Date" (day of the month)
$ i2cget -y 1 0x68 4
0x14
Using i2cget, view indexed register 0 "Seconds"
$ i2cget -y 1 0x68 0
0x05
Using i2cget, view indexed register 0 "Seconds"
$ i2cget -y 1 0x68 0
0x07
Using i2cset, change indexed register 4 "Date" (day of the month) to 25
$ i2cset -y 1 0x68 4 0x25
Display the indexed register's new value
$ i2cget -y 1 0x68 4
0x25