About Sed Simulator

Interactive sed command simulator. Part of the DevTools Surf developer suite. Browse more tools in the Developer Utilities collection.

Use Cases

• Replace all occurrences of a string across a file in a single command.
• Delete lines matching a pattern from a log file.
• Insert or append text at specific line numbers in a file.
• Chain multiple substitutions in a single sed command for batch text transformation.

Tips

• Use -E flag (extended regex) for +, ?, and () without escaping — basic regex requires \+, \?, and \(\) which is easy to confuse.
• Test destructive substitutions with p flag first: sed -n 's/old/new/p' shows what would change without modifying anything.
• Use \n in replacement strings to insert literal newlines on GNU sed (macOS sed requires a different escape syntax).

Fun Facts

• sed was created by Lee McMahon at Bell Labs in 1973, making it one of the oldest Unix utilities still in daily use. The name stands for 'stream editor.'
• sed's s command (substitute) is the most used sed feature by far — many sed users have never needed any other command despite sed having a complete set of programming constructs.
• POSIX standardized sed in 1992. GNU sed added extensions (like -E for extended regex and in-place editing with -i) that are not POSIX-compliant but became de facto standards.

FAQ

How do I do in-place file editing with sed?

Use sed -i 's/old/new/g' file.txt on GNU/Linux. On macOS (BSD sed), use sed -i '' 's/old/new/g' file.txt — the empty string after -i is required. Always backup before -i on critical files.

What's the difference between sed s/x/y/ and s/x/y/g?

Without /g, the substitution applies only to the first match on each line. With /g (global), it applies to every match on each line. This is the most common sed mistake.