Additive color mixing begins with black and ends with white; as more color is added, the result is lighter and tends to white. The RGB colors are light primaries and colors are created with light. Percentages of red, green, & blue light are used to generate color on a computer screen.
In shell scripting we often need to check if file or directory exists and take appropriate action. This post show you how to check it and how this check use in your script. For checking we will use file test operators -f for file and -d for directory, which return TRUE if file or directory exists. And here is output of the script.
In addition to typing commands directly to the shell, you can place them in a file (which must be given execute permission), and then run the file. A file containing UNIX shell commands is known as a script (or shell script). Executing the script is equivalent to typing the commands within it. The Unix shells are actually quite sophisticated programming languages in their own right: there are entire books devoted to programming in them.