sed

Overview

sed (stream editor) transforms text line by line — substitute, delete, print, and simple inserts — without opening an interactive editor. GNU sed is common on Linux.

Syntax

sed [options] 'script' [file...]
sed [options] -e 'script' -e 'script' [file...]
sed [options] -f script.sed [file...]

Common Options

Option	Description
-n	Quiet; only explicit prints
-E / -r	Extended regex
-i[SUFFIX]	In-place edit (optional backup suffix)
-e	Multiple scripts
-f	Script file

Common Commands (in script)

Cmd	Meaning
s/pat/repl/flags	Substitute (g, i, p)
d	Delete line
p	Print
a/i/c	Append/insert/change
q	Quit

Safety

sed -i rewrites files — keep backups (-i.bak) until trusted. Quoting matters: prefer single quotes around scripts; use '\'' to embed a single quote.

Examples with Explanations

Substitute first match per line

sed 's/foo/bar/' file.txt

Global substitute

sed 's/foo/bar/g' file.txt

Extended regex

sed -E 's/[0-9]{1,3}(\.[0-9]{1,3}){3}/IP/g' access.log

Delete matching lines

sed '/^#/d; /^$/d' config.txt

Print only matches (like grep with rewrite)

sed -n 's/.*ERROR: //p' app.log

In-place with backup

sed -i.bak 's/Enable=false/Enable=true/' app.conf

Line ranges

sed -n '10,20p' file.txt
sed '1,5d' file.txt

Multiple expressions

sed -e 's/\r$//' -e 's/[ \t]\+$//' file.txt

Notes & Pitfalls

• Default regex is BRE; +/| need escapes unless -E.
  
• & in replacement is the whole match; use \& for literal.
  
• Binary files: do not sed -i blindly.
  
• Complex multi-line edits are awkward — consider perl -0pe or an editor.

Related Commands

• awk — field-oriented
  
• grep — filter only
  
• tr — character classes
  
• perl -pe — richer substitutions
  
• ed/ex/vim — full editors

Additional Resources

• man sed
  
• GNU sed manual