Program Source Code Many of the command-line programs found on Unix-like systems were cre- ated to support system administration and software development, and text- processing programs are no exception. Many of them are designed to solve software development problems. The reason text processing is important to software developers is that all software starts out as text. Source code, the part of the program the programmer actually writes, is always in text format. Revisiting Some Old Friends Back in Chapter 6, we learned about some commands that are able to accept standard input in addition to command-line arguments. We touched on them only briefly then, but now we will take a closer look at how they can be used to perform text processing. cat--Concatenate Files and Print on Standard Output The cat program has a number of interesting options. Many of them are used to better visualize text content. One example is the -A option, which is used to display non-printing characters in the text. There are times when we want to know if control characters are embedded in our otherwise visible text. The most common of these are tab characters (as opposed to spaces) and car-