A Stream EDitor ( SED ) tool is used to filter text that it gets from a pipeline feed. You do not need to interact with the editor while it is running; that is why sed is sometimes called a batch editor. This feature allows use of editing commands in scripts, greatly easing repetitive editing
Bash Regular Expressions
A regular expression is a pattern that describes a set of strings. Regular expressions are constructed analogously to arithmetic expressions by using various operators to combine smaller expressions.