Too long; didn't read (TL;DR) is a flippant Internet acronym for a summary that first came into use about a decade ago. It seems to be falling out of fashion but survives in tldr, the newest command and format for computer documentation. It is far from the first documentation command, but it fills a niche as a cheat sheet for the most common options for commands.

The most common documentation format, of course, is the man page, which dates back to 1971 (Figure 1). Man pages cover commands, libraries, and configuration files, usually aiming for an encyclopedia-like summary of their topics. One great advantage is that the pages are highly organized, arranged in nine sections ranging from user commands and system calls to system administration calls, kernel routines, and daemons. Each page presents information in a rigid format divided into further sections (see Table 1), although not all sections are mandatory. The Examples, Notes, and Bugs sections, for example, are frequently omitted. This consistent structure compensates for the often overwhelming detail of some man pages, which can be over 1,000 lines long.

GNU projects provide Info pages that have a similar purpose to man pages and often use more user-friendly language. However, they can be less structured and concise and have not caught on nearly as much. In fact, even GNU projects often maintain both formats. The main advantage of Info pages is that they can be read in Emacs using a mouse.

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