A program in a directory can be started by typing its name if your shell variable PATH includes that directory, otherwise you have to prepend the whole path. The directory that you are in after you logged in is called the login- or home directory. If you want to exclude certain characters to be replaced then you have to specify the set of characters that can be replaced. Such a set is enclosed in brackets. The bracket syntax recognizes ranges.
Ranges use hyphens to separate the start and end values.
These special characters are called wildcards . In Unix we distinguish three file permissions. Use the Unix tutorial to learn about file protection. Describe how to change this protection so that the file is only readable for you, the owner. Show the output.