Introduction to Text Manipulation

sed (Stream Editor) is a powerful, non-interactive text editor that processes input line by line, performing transformations (like searching and replacing).

The Substitution Command (s)

The most common use of sed is substitution, using the format: s/pattern/replacement/flags.

Basic Substitution (First Occurrence)

Replace the first occurrence of 'old' with 'new' on each line:

bash $ echo 'old file old config' | sed 's/old/new/' new file old config

Global Substitution (g flag)

To replace all occurrences on a line, use the g (global) flag.

bash $ echo 'old file old config' | sed 's/old/new/g' new file new config

In-Place Editing (-i)

By default, sed prints the result to STDOUT. The -i option modifies the file directly (in-place).

bash

Permanently change 'localhost' to '127.0.0.1' in my_config.txt

$ sed -i 's/localhost/127.0.0.1/g' my_config.txt