REFERENCES

Links:
https://www.gnu.org/software/libc/manual/html_node/Implementing-a-Shell.html
https://gist.github.com/aspyct/3462238
https://stackoverflow.com/questions/916900/having-trouble-with-fork-pipe-dup2-and-exec-in-c
https://stackoverflow.com/questions/12733105/c-function-that-counts-lines-in-file
https://unix.stackexchange.com/questions/266794/does-the-shell-fork-when-i-use-built-in-commands/266824#266824
https://stackoverflow.com/questions/12765010/c-test-for-file-existence-before-calling-execvp/12765185
https://stackoverflow.com/questions/4992108/getcwd-second-parameter
https://stackoverflow.com/questions/4291080/print-the-environment-variables-using-environ
https://stackoverflow.com/questions/29621/change-own-process-priority-in-c
https://stackoverflow.com/questions/29621/change-own-process-priority-in-c