Linux

sort and uniq are the classic pair for working with lists of text lines. sort arranges lines in order; uniq collapses repeated lines. They’re almost always used together, because uniq only works correctly on sorted input. Key point: uniq compares adjacent lines only. If duplicates aren’t next to each other, uniq won’t remove them. That’s…

cut, paste, and join are the column-level tools of the Unix text toolbox. cut pulls fields out of each line, paste puts lines from multiple files side by side, and join combines two files on a shared key — like a miniature SQL join at the command line. Key point: These tools work on structured…

comm and diff both compare files, but they answer different questions. comm asks “which lines are shared and which are unique?” — it’s a set operation on two sorted files. diff asks “what exactly changed, line by line?” — it’s a detailed comparison that shows you the edits. Key point: comm requires sorted input and…

patch and tr sit at opposite ends of the text-processing spectrum. patch applies a diff file to an original — it’s how software updates and bug fixes are distributed. tr translates or deletes individual characters from a stream — it’s the simplest character-level filter on Linux. Key point: patch works together with diff. diff produces…

aspell is a command-line spell checker. It can check a whole file interactively, check individual words or sentences piped in from stdin, or filter text in special formats like HTML, email, or LaTeX. It supports dozens of languages and several suggestion modes. Key point: aspell is the successor to ispell and is generally more accurate…