Open source is all about code. Contributors read tons of code, of which they have written only a small fraction. Being able to comprehend a program is crucial to the contribution process, and free software is all about contribution. In other words, you need tools to read and understand code.

These tools are called "source code browsers" or "source navigators." Linux has many of them, and normally they fall in two large categories. Older ones implement their own (simplified) parsers to recognize language symbols, such as function definitions, and record their location in the source code. This works fast and reasonably well, yet most programming languages have complex grammar that simplified parsers can't fully embrace. Newer browsers rely on the tool set to build an abstract syntax tree (AST) [1]. This makes indexing more precise, but also slower and more cumbersome to generate. Choosing one approach over another depends on the situation, and I hope this text provides you with some guidance.

Ubiquitous Ctags

Ctags is the de facto standard for source code indexers in Linux. As the name suggests, it builds on the "tag" concept. Put simply, a tag is a syntax construct that has an index entry, such as a class, function, or macro definition. This index comes in a so-called "tags" file, and the main purpose of the non-interactive ctags command is to generate tags files from source-code trees. Tags files have a well-defined format, and virtually all code editors in Linux understand it.

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