How to raise and take care of shell scripts: regular expressions

Regular expressions

It's a fascinating but also confusing field. Regular expressions are extremly powerful to analyse character sequences (keep in mind, that in the shell - like in all programming languages which do not difference between the various types of variables - all values are characters, ... or integers, ... or something else; it's in the mood of the programmer). To complete the confusion the regular expressions already bring with themselves, there are different kinds of them: basic regular expressions, extended regular expressions, perl compatible regular expressions and probably a whole number of language dependent regular expressions.
If you stay within the shell, you have only to deal with the first two kinds. I strongly recommend to study regular expressions in detail because of their large variety of different ways to analyse and process input. Look at the web, study man 7 regex and most important: practice, practice, practice!