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Usage

Meaning

sed means *Stream EDitor*.

Main options

-e

-e allows sequential execution of several instruction sets.

-i

-i allows the input file to be modified

Principle

Sed works with 4 zones :

• input (IN)
• pattern space (PS)
• output (OUT)
• hold space (HS)

INPUT	PATTERN SPACE	OUTPUT
	HOLD SPACE Storage memory contains at least '\n'

Syntax

$ sed 'command' file

Processing

1. sed copies the first line of the input file in the pattern space
2. sed applies the command(s) in between quotes to the pattern space
3. sed moves the pattern space content to the output
4. sed goes to the next line of the file and repeats operation 1

Main commands

For the pattern space

Command	Description
p	prints PS content
d	deletes PS content
=	prints PS line number
n	moves PS to OUT and IN to PS
N	copies next line from IN to PS
P	prints first line of PS to OUT
D	deletes first line of PS
s/x/y	replaces x by y in the PS
s/x/y/p	idem then prints PS content
s/x/y/g	(GLOBAL) idem but replaces as much as possible
s/x/y/I	idem but case-insensitive
y/abc/def	replaces characters a, b, c by d, e, f respectively
w example	writes in file
s/x/y/w file	idem and write the modified lines in the file
r file	copies file's content in the PS
q	stops execution and moves PS to OUT
Q	stops execution, does not perform stages 3 and 4
#	comment
a	APPEND - appends a line after
i	INSERT - appends a line before
c	CHANGE - change the line (idem Vim)

For the hold space

Command	Description
x	swaps PS and HS
h	HOLD - copies PS to HS
g	GET - moves HS to PS
H	adds PS to HS
G	adds HS to PS

Debugging

Debugging can be done with 'l' command. It prints PS then breaks. To print the PS after command processing, use the following:

$ sed 'n; l;' file

Labels

The command ':' defines a label that can be reused with command 'b' (BRANCH)

• 't' goes to the label if a replacement has been done
• 'T' goes to the label if no replacement has been done