Using GPIOs Within a Linux Context

Interracting with GPIOs within a shell (Bash Shell)

Interracting with GPIOs within a shell script (Bash Shell)

Interracting with GPIOs within a C / C++ Program - Using system() calls

Interracting with GPIOs within a C / C++ Program - sysfs interraction

Interracting with GPIOs within a C / C++ Program using Memory Mapped GPIO

A collection of a few links that may help you understand this subject better

Further Reading