sed - stream editor for filtering and transforming text

Options you will use

-n

Suppress automatic printing; print only what p asks for.

-i[SUFFIX]

Edit files in place. -i.bak keeps a backup - do that on anything under /etc.

-E, -r

Extended regular expressions.

-e SCRIPT

Add another script; use it more than once for multiple commands.

s/RE/REPL/[gi]

Substitute. g = every occurrence on the line, i = case-insensitive. & is the whole match, \1 a capture group.

ADDR{,ADDR}cmd

Address: a line number, $ for last, /regex/, or a range like 3,6 or /start/,/end/.

d p q = a i c y

delete, print, quit, print line number, append, insert, change, transliterate.

-i[SUFFIX], --in-place[=SUFFIX]

Edit the file in place; with a SUFFIX (-i.bak) keep a backup copy first.

Examples

$ sudo sed -i.bak 's/read.timeout.ms=0/read.timeout.ms=5000/' /etc/orders/app.conf

in-place edit with a backup

$ sed -n '3,6p' file

print lines 3 to 6

$ sed '/^#/d;/^$/d' /etc/fstab

strip comments and blank lines

$ sed -i 's|^/swap.img|#&|' /etc/fstab

comment out a line; | as the delimiter avoids escaping slashes

Gotchas

• sed -i needs write permission on the DIRECTORY (it writes a temp file and renames it), not just on the file.

Taught in

• 15.40 Imperative vs declarative: create, apply, diff, patch, replace, edit
• 18.6 kubeadm init and join: what they actually do
• 19.3 The speed kit: alias, $do, generators, editors, explain