Regular expressions (regex) are the language of pattern matching on Linux. They let you describe what you’re looking for — not the exact characters — and every major text tool understands them: grep, sed, awk, find, and even the shell itself. Learn regex once and you’ll use it everywhere. Key point: There are two dialects…
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…
sed (stream editor) is the most versatile text-transformation tool on Linux. It reads input line by line, applies a script of editing commands, and writes the result to stdout. It can substitute, delete, insert, append, and print — all without opening an editor. Key point: sed works on a stream — a file, a pipe,…
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…
nl, fold, and fmt are three small but useful text-formatting tools. nl numbers lines; fold breaks long lines at a fixed width; fmt reflows paragraphs to a target width. They’re the kind of commands you reach for when you need to make raw text readable — for reports, citations, or terminal output. Key point: fold…
pr and printf are two very different formatting tools. pr takes text and prepares it for printing — paginating it, adding headers, arranging it into columns. printf takes a format string and data, and produces precisely formatted output — it’s the shell’s answer to C’s printf(). Key point: pr is about layout on a page….
groff is the GNU implementation of the classic Unix troff typesetting system. It takes plain text with embedded formatting macros and produces typeset output — plain text, PostScript, PDF, HTML, or UTF-8. Its most important modern job is rendering man pages, but it can also produce nicely formatted documents. Key point: groff is a formatter,…
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