Sed Cheatsheet

The sed (stream editor) command processes text streams line by line, applying specified operations to each line. It follows a pattern-action paradigm where you specify what to match and what action to take when a match is found.

Pattern matching in sed allows you to select which lines to operate on. Patterns can be regular expressions, line numbers, or ranges. When a pattern matches, sed applies the associated command to that line or range.

The substitution command (s) is one of sed's most powerful features, allowing you to replace text matching a pattern with new content. It supports various flags, capture groups, and special characters to handle complex text transformations.

The delete command (d) is one of sed's most powerful operations, allowing you to remove specific lines from text streams based on patterns, line numbers, or ranges. It operates on the pattern space and immediately starts the next cycle without printing the current pattern space.

Text insertion commands in sed allow you to add new content to files. The append (a), insert (i), and change (c) commands are the primary methods for adding text, each with different placement behavior.

Text transformation in sed involves commands that modify text content beyond simple substitution. These operations include case conversion, character transformations, line joining, and buffer manipulations that enable complex text rearrangements.

Sed can interact with external files beyond its standard input/output streams. These operations allow reading from files during processing, writing output to separate files, and handling multiple input files efficiently.

Sed normally processes text line by line, but multi-line operations allow working with multiple lines as a single pattern space. This enables complex transformations like joining lines, multi-line pattern matching, and block-based processing.

Control flow in sed allows for conditional execution, branching, and early termination of scripts. These features transform sed from a simple stream editor into a powerful text processing language with programming-like capabilities.

Creating maintainable sed scripts involves proper organization, documentation, and testing strategies. Well-structured scripts are easier to debug, reuse, and share with others.