Overview

sed (stream editor) is a non-interactive command-line utility that reads text line by line, applies a script of editing commands, and writes the result to standard output. It has shipped with every Unix-like system since the 1970s and remains one of the most portable text-processing tools available.

What sed Provides

sed processes text as a stream: it reads one line at a time into its pattern space, applies commands in the order they appear in the script, then either prints the pattern space or discards it and moves to the next line. This line-oriented, non-interactive model makes sed ideal for automated text transformation in shell scripts and pipelines.

Key Concepts

• Stream editing: Text flows through sed one line at a time without loading the entire file into memory
• Addresses: Numeric line numbers, regex patterns, or ranges that restrict which lines a command applies to
• Commands: Single-character instructions (s, d, p, a, i, c, y, q, etc.) that transform the current line
• Pattern space: The working buffer holding the current line being processed
• Hold space: A secondary buffer used to save and retrieve text across line boundaries
• Regular expressions: POSIX basic regex (BRE) by default; extended regex (ERE) with -E
• In-place editing: The -i flag rewrites a file directly, optionally creating a backup

Content in This Section

• By Example — Learn sed through 85 heavily annotated examples covering substitution, deletion, insertion, addressing, regular expressions, hold space, branching, and real-world text processing.