Resources: Linux

There are many aspects to a Linux system.

• At the lowest level, it is an operating system kernel that implements the POSIX API (Application Programmer Interface) via system calls or traps. Basic components include processes, file systems, and networking. This is documented in section 2 of the online manual (man).
• Supporting the system calls are programming languages and higher-level libraries (section 3 of the man pages).
• Linux is also is the complete set of myriad utility programs, scripting languages, and editors that allow useful work to be performed (section 1 of the man pages).
• The CLI (Command-Line Interface), aka "the shell". There are a variety of shell programs, the most common of which are
  • bash (Bourne-Again Shell), which is inspired by the original sh written by Stephen Bourne, and
  • tcsh, which is based on csh which was developed for the BSD Unix variant.
  Shell programs have no special capabilities to interact with the system beyond those of any application program. The heavy lifting is done through the same system calls and libraries accessible to any other application. While shells are designed to manage the execution of other programs, most shells provide some programming capabilities, including loops and conditionals. A shell script is typically a program that invokes other programs with control flow based on the exit status of those programs.

One of the key concepts in Unix-based systems is the pipeline, where output from one program can be fed as input to another. A filter is a (typically small, single-function) utility program that is designed to work in a pipeline with other program.

The Perl programming language was insprired by the Unix utilities and many of the utilities can be replaced by a short, often single-line, Perl script.

It's worthwhile to learn both vi (or its modern incarnation, vim) and emacs because both are designed to maximize programmer efficiency, based on different approaches (vi based on minimizing keystrokes and emacs based on programmability). With minimal understanding, vi looks ugly and confusion; with deeper understanding it looks positively elegant. Even if you prefer an IDE like Visual Studio or Eclipse, it is worthwhile learning vim.

Books

• Linux Cookbook
• bash Cookbook: Solutions and Examples for bash Users
• Linux in a Nutshell,
  • Generally, O'Reilly Media publishes high-quality technology books

Web

• University of Washington: Using Unix Computers
• O'Reilly Media Linux command directory