There are only a few special characters involved in working with character strings on the command line or in a script on Linux: the single quote, the double quote and the backslash. But the rules aren’t as obvious as one might think. In this post, we’ll look at the easy and the somewhat tricky uses of these special characters.
The echo command doesn’t require any variety of quote characters much of the time. You can echo a phrase like this without bothering with quotes of any kind.
Source:: Network World – Data Center