In the previous chapter, we saw that we could make use of sed to edit files from within our scripts. The sed command is the Stream Editor and opens the file line by line to search or edit the file contents. Historically, this goes way back to Unix where systems may not have had enough RAM to open very large files. Using sed was absolutely required to carry out edits. Even today, we will use sed to make changes and display data from files with hundreds and thousands of entries. It is simpler and easier and more reliable than a human trying to do the same thing. Most importantly, as we have seen, we can use sed in scripts to edit the files automatically, no human interaction is required.

We will start by looking at grep and search the files for text. The re in grep command is short for Regular Expression. This introduces the power of POSIX Compliant Regular Expressions before we look at sed. Even though we are not looking at scripting in this chapter, we will be...