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,…
pr, lpr, and lp cover the three stages of printing on Linux: pr formats text for a page, lpr and lp send files to a printer. lpr is the Berkeley-style command; lp is the System V-style command. Both talk to CUPS — the Common UNIX Printing System that almost every Linux distro uses today. Key…
These three commands are the print management trio on Linux. lpstat tells you about the printers — which ones exist, which are accepting jobs, which is the default. lpq shows you the queue — what’s waiting to print. lprm lets you remove jobs from the queue. Key point: All three work with CUPS (Common UNIX…
A shell script is a plain-text file full of shell commands that the system runs for you, in order, automatically. Instead of typing the same sequence of commands over and over, you write them once and run the script. It’s the simplest form of programming on Linux — and one of the most useful. Key…
Variables are the foundation of any shell script. They let you store values, pass data around, and make your scripts flexible instead of hardcoded. Shell scripts also come with a set of special variables that the shell fills in automatically — the script name, arguments, process ID, and exit status. Key point: In shell scripting,…
Outputting text is the most basic thing a shell script does. You can use echo for simple messages, printf when you need precise formatting, and here documents when you need to pass a block of multi-line text to a command. Key point: echo is quick and convenient but behaves differently across shells. printf is predictable…
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