Transcript Lecture 9 sed sed  sed   is a stream-oriented editor the input (file/std input) flows through the program sed and is directed the standard output Used primarily.

Lecture 9
sed
sed
 sed


is a stream-oriented editor
the input (file/std input) flows through the
program sed and is directed the standard
output
Used primarily for non interactive operations
[-n] –f script_file file or
sed [-n] `command` file
 sed


sed executes the given command or script file
that contain commands on each line of the
input (file)
-n: turn off default printing
sed Commands

p: print line






-n prevents lines from being printed twice
d: delete line
s/old/new/: substitute old with new
s/old/new/g: substitute all occurrences of old
with new
!: negates a command
Full list of commands can be found on page 129
sed Examples
 sed
p file.txt
 sed –n p file.txt
 sed d file.txt
 sed \!d file.txt
 p and d seem a bit worthless, don’t they?
They purpose will become more clear
when we discuss addresses.
sed: Substitution
 The
strongest feature of sed
 Syntax is s/expression/string/flag


expression is a regular expression
string is a string
 sed

‘s/|/:/’ data.txt
substitute the character ‘|’ with the character
‘:’
 sed
‘s/|/:/g’ data.txt
Some Useful Substitution Flags
 g: global
 p:



(replace all matches on the line).
print the line if a successful match
sed ‘s/old/new/g’ file.txt
sed ‘s/old/new/gp’ file.txt
sed –n ‘s/old/new/gp’ file.txt
Regular Expressions for sed
 The

A

usual suspects
^, $, ., *, [ ], [^ ], \( \), \<, \>
new operator
&: the string which matches the expression
• can be used in the substitution string
• s/hello/**&**/g replaces all occurrences of hello
with **hello**
sed Addressing

So far, we have been applying sed commands to
every line

makes p and d not very useful

With addressing, we can apply commands to
some, but not all lines
 sed can use




0 addresses (all lines)
1 address (a single line)
2 addresses (a range of lines)
Address can be line numbers of context (defined
by regular expressions)
Line Number Addressing Examples
%sed –n ‘3,4p’ foo.txt
Since sed prints each line anyway, if we only
want lines 3 & 4 (instead of all lines with lines
3 & 4 duplicated) we use the –n
%sed –n ‘$p’ foo.txt
For each line, if that line is the last line, print
%sed –n ‘3,$p’ foo.txt
For each line, if that line is the third through
last line, print
Context Addressing Examples
 Use
patterns/regular expressions rather
than explicitly specifying line numbers
%sed –n ‘/^From: /p’ $HOME/mbox
 retrieve all the sender lines from the mailbox
file, i.e., for each line, if that line starts with
‘From’, print it. Note that the / / mark the
beginning and end of the pattern to match
%ls –l | sed –n ‘/^.....w/p’

For each line, if the sixth character is a W,
print
Context Ranges
 sed

‘/hello/,/there/d’ file.txt
delete all lines that occur between a line that
matches hello and a line that matches there.
The hello and there lines are also removed.
 Multiple

contexts are possible
two contexts specified by a single range
sed Addressing
 Using
a ! after the address means all lines
which do not match the address

sed ‘1\!d’ test.txt
Example file
northwest
western
southwest
southern
southeast
eastern
northeast
north
central
NW
WE
SW
SO
SE
EA
NE
NO
CT
sed ‘/north/p’ file
sed ‘3,$d’ file
sed ‘s/west/north/g’ file
sed '/north/a\
hello,word' datafile
Charles Main
Sharon Gray
Lewis Dalsass
Suan Chin
Patricia Heme
TB Savage
AM Main Jr.
Margot Webber
Ann Stephens
3.0
5.3
2.7
5.1
4.0
4.4
5.1
4.5
5.7
.98
.97
.8
.95
.7
.84
.94
.89
.94
3
5
2
4
4
5
3
5
5
sed –n ‘s/west/north/g’ file
sed ‘s/\(Mar\)got/\1ianne/p’ file
sed ‘/west/,/east/s/$/**VACA**/’ file
34
23
18
15
17
20
13
9
13
sed: Using files
 Tedious
to type in commands at the prompt,
especially if commands are repetitive
 Can put commands in a file and sed can use
them
 sed –f cmds.sed data.txt
file with commands
sed scripts
 Series
of commands can be put in a file
and use the ‘-f’ option.
 Can also create an sed script:
s/vi/emacs/g
/[Ww]indows/d
p
Another Example
 sed
script to remove all HTML tags from a
file:
s/<[^>]*>//g
p
Reading Assignment
 Chapter
5