This series started with an overview of Linux fundamentals and a look at some important concepts behind shells. Let’s continue looking at obscure features of Linux that books generally don’t cover but that wizards should know. Read on to find out more about the standard I/O system. Though the ideas behind standard I/O are common knowledge, let’s start with an introduction to get on the same page (so to speak).
What’s behind standard I/O?
Back in the days when Unix was new, the idea of standard I/O wasn’t commonplace. It wasn’t necessarily simple to write data to different devices - a program might need different code to read or write files, tapes, terminals and printers. Users were accustomed to seeing progress messages and summaries.
A well-behaved Unix/Linux utility outputs only valid data. If there’s no trouble and no data, there’s no output. For instance, if grep doesn’t find matching text, it doesn’t output “No match found.” It simply terminates.
Unix popularized the idea that data can be a stream of bytes, that a program reads and writes without knowing where the data is coming from or where it’s going. The operating system and its device drivers convert a stream of bytes to and from the correct formats for all of the system’s devices (disks, printers, tape drives, and so on), letting the programs handle the data. The Unix operating system and the shell also arrange the “plumbing” that routes data between processes and devices - for instance, by doing…
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