Linux Fledglings

Consider you have a file called dictionary.txt with a huge collection of words and you only want to view line containing the word "tux". To check each word line by line is a tedious task, instead we use the grep command.

When you come across a new word and don't know what it means, you will start looking for its meaning in a dictionary. But what if you have  just heard about a new Linux command and have absolutely no idea what the command does? Where will you look for a reference or documentation to the command?