There are many ways to extract substrings from lines of text using Linux and doing so can be extremely useful when preparing scripts that may be used to process large amounts of data. This post describes ways you can take advantage of the commands that make extracting substrings easy.
Using bash parameter expansion
When using bash parameter expansion, you can specify the starting and ending positions for the text that you want to extract. For example, you can create a variable by assigning it a value and then use syntax like that shown below to select a portion of it.
Source:: Network World – Linux