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<!DOCTYPE html><html><body><title>Sed Tutorial</title>

<h1>Sed Tutorial</h1>

This tutorial takes you through all about Stream EDitor (Sed), one of the most prominent text-processing utilities on GNU/Linux. Similar to many other GNU/Linux utilities, it is stream-oriented and uses simple programming language. It is capable of solving complex text processing tasks with few lines of code. This easy, yet powerful utility makes GNU/Linux more interesting.

<h1>Audience</h1>

If you are a software developer, system administrator, or a GNU/Linux loving person, then this tutorial is for you.

<h1>Prerequisites</h1>

You must have basic understanding of GNU/Linux operating system and shell scripting.

<title>Stream Editor - Overview</title>

<h1>Stream Editor - Overview</h1>

The acronym SED stands for Stream EDitor. It is a simple yet powerful utility that parses the text and transforms it seamlessly. SED was developed during 1973–74 by Lee E. McMahon of Bell Labs. Today, it runs on all major operating systems.

McMahon wrote a general-purpose line-oriented editor, which eventually became SED. SED borrowed syntax and many useful features from ed editor. Since its beginning, it has support for regular expressions. SED accepts inputs from files as well as pipes. Additionally, it can also accept inputs from standard input streams.

SED is written and maintained by the Free Software Foundation (FSF) and it is distributed by GNU/Linux. Hence it is often referred to as GNU SED. To a novice user, the syntax of SED may look cryptic. However, once you get familiar with its syntax, you can solve many complex tasks with a few lines of SED script. This is the beauty of SED.

<h2>Typical Uses of SED</h2>

SED can be used in many different ways, such as:

<title>Stream Editor - Environment</title>

<h1>Stream Editor - Environment</h1>

This chapter describes how to set up the SED environment on your GNU/Linux system.

<h2>Installation Using Package Manager</h2>

Generally, SED is available by default on most GNU/Linux distributions. Use which command to identify whether it is present on your system or not. If not, then install SED on Debian based GNU/Linux using apt package manager as follows:

After installation, ensure that SED is accessible via command line.

On executing the above code, you get the following result:

Similarly, to install SED on RPM based GNU/Linux, use yum package manager as follows:

After installation, ensure that SED is accessible via command line.

On executing the above code, you get the following result:

<h2>Installation from Source Code</h2>

As GNU SED is a part of the GNU project, its source code is available for free download. We have already seen how to install SED using package manager. Let us now understand how to install SED from its source code.

The following installation is applicable to any GNU/Linux software, and for most other freely-available programs as well. Here are the installation steps:

Download the source code from an authentic place. The command-line utility wget serves this purpose.

Decompress and extract the downloaded source code.

Change into the directory and run configure.

Upon successful completion, the configure generates Makefile. To compile the source code, issue a make command.

You can run the test suite to ensure the build is clean. This is an optional step.

Finally, install the SED utility. Make sure you have superuser privileges.

That is it! You have successfully compiled and installed SED. Verify it by executing the sed command as follows:

On executing the above code, you get the following result:

[jerry]$ sudo apt-get install sed

</pre>

After installation, ensure that SED is accessible via command line.

[jerry]$ sed --version

</pre>

On executing the above code, you get the following result:

sed (GNU sed) 4.2.2

License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.

This is free software: you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law.

Written by Jay Fenlason, Tom Lord, Ken Pizzini,

and Paolo Bonzini.

GNU sed home page: <http://www.gnu.org/software/sed/>.

General help using GNU software: <http://www.gnu.org/gethelp/>.

E-mail bug reports to: <bug-sed@gnu.org>.

Be sure to include the word "sed" somewhere in the "Subject:" field.

</pre>

Similarly, to install SED on RPM based GNU/Linux, use yum package manager as follows:

[root]# yum -y install sed

</pre>

After installation, ensure that SED is accessible via command line.

[root]# sed --version

</pre>

On executing the above code, you get the following result:

GNU sed version 4.2.1

This is free software; see the source for copying conditions. There is NO

warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE,

to the extent permitted by law.

GNU sed home page: <http://www.gnu.org/software/sed/>.

General help using GNU software: <http://www.gnu.org/gethelp/>.

E-mail bug reports to: <bug-gnu-utils@gnu.org>.

Be sure to include the word "sed" somewhere in the "Subject:" field.

</pre>

<h2>Installation from Source Code</h2>

The following installation is applicable to any GNU/Linux software, and for most other freely-available programs as well. Here are the installation steps:

<li>Download the source code from an authentic place. The command-line utility wget serves this purpose.</li>

[jerry]$ wget ftp://ftp.gnu.org/gnu/sed/sed-4.2.2.tar.bz2

</pre>

<li>Decompress and extract the downloaded source code.</li>

[jerry]$ tar xvf sed-4.2.2.tar.bz2

</pre>

<li>Change into the directory and run configure.</li>

[jerry]$ ./configure

</pre>

<li>Upon successful completion, the configure generates Makefile. To compile the source code, issue a make command.</li>

[jerry]$ make

</pre>

<li>You can run the test suite to ensure the build is clean. This is an optional step.</li>

[jerry]$ make check

</pre>

<li>Finally, install the SED utility. Make sure you have superuser privileges.</li>

[jerry]$ sudo make install

</pre>

</ul>

That is it! You have successfully compiled and installed SED. Verify it by executing the sed command as follows:

[jerry]$ sed --version

</pre>

On executing the above code, you get the following result:

sed (GNU sed) 4.2.2

License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.

This is free software: you are free to change and redistribute it.

There is NO WARRANTY, to the extent permitted by law.

Written by Jay Fenlason, Tom Lord, Ken Pizzini,

and Paolo Bonzini.

GNU sed home page: <http://www.gnu.org/software/sed/>.

General help using GNU software: <http://www.gnu.org/gethelp/>.

E-mail bug reports to: <bug-sed@gnu.org>.

Be sure to include the word "sed" somewhere in the "Subject:" field.

</pre>

<title>Stream Editor - Workflow</title>

<h1>Stream Editor - Workflow</h1>

In this chapter, we will explore how SED exactly works. To become an expert SED user, one needs to know its internals. SED follows a simple workflow: Read, Execute, and Display. The following diagram depicts the workflow.

Read: SED reads a line from the input stream (file, pipe, or stdin) and stores it in its internal buffer called pattern buffer.

Execute: All SED commands are applied sequentially on the pattern buffer. By default, SED commands are applied on all lines (globally) unless line addressing is specified.

Display: Send the (modified) contents to the output stream. After sending the data, the pattern buffer will be empty.

The above process repeats until the file is exhausted.

<h2>Points to Note</h2>

Pattern buffer is a private, in-memory, volatile storage area used by the SED.

By default, all SED commands are applied on the pattern buffer, hence the input file remains unchanged. GNU SED provides a way to modify the input file in-a-place. We will explore about it in later sections.

There is another memory area called hold buffer which is also private, in- memory, volatile storage area. Data can be stored in a hold buffer for later retrieval. At the end of each cycle, SED removes the contents of the pattern buffer but the contents of the hold buffer remains persistent between SED cycles. However SED commands cannot be directly executed on hold buffer, hence SED allows data movement between the hold buffer and the pattern buffer.

Initially both pattern and hold buffers are empty.

If no input files are provided, then SED accepts input from the standard input stream (stdin).

If address range is not provided by default, then SED operates on each line.

<h3>Examples</h3>

Let us create a text file quote.txt to contain a quote of the famous author Paulo Coelho.

To understand the workflow of SED, let us display the contents of the file quote.txt using SED. This example simulates the cat command.

When the above code is executed, it will produce the following result.

In the above example, quote.txt is the input file name and before that there is a pair of single quote that implies the SED command. Let us demystify this operation.

First SED reads a line from the input file quote.txt and stores it in its pattern buffer. Then it applies SED commands on the pattern buffer. In our case, no SED commands are there, hence no operation is performed on the pattern buffer. Finally it deletes and prints the contents of the pattern buffer on the standard output. Isn't it simple?

In the following example, SED accepts input from the standard input stream.

When the above code is executed, it will produce the following result.

Here, the first line is entered through keyboard and the second is the output generated by SED. To exit from the SED session, press ctrl-D (^D).

[jerry]$ vi quote.txt

There is only one thing that makes a dream impossible to achieve: the fear of failure.

- Paulo Coelho, The Alchemist

</pre>

To understand the workflow of SED, let us display the contents of the file quote.txt using SED. This example simulates the cat command.

[jerry]$ sed '' quote.txt

</pre>

When the above code is executed, it will produce the following result.

There is only one thing that makes a dream impossible to achieve: the fear of failure.

</pre>

In the above example, quote.txt is the input file name and before that there is a pair of single quote that implies the SED command. Let us demystify this operation.

In the following example, SED accepts input from the standard input stream.

[jerry]$ sed '' <press enter>

</pre>

When the above code is executed, it will produce the following result.

There is only one thing that makes a dream impossible to achieve: the fear of failure.

</pre>

<title>Stream Editor - Basic syntax</title>

<h1>Stream Editor - Basic Syntax</h1>

This chapter introduces the basic commands that SED supports and their command-line syntax. SED can be invoked in the following two forms:

The first form allows to specify the commands in-line and they are enclosed within single quotes. The later allows to specify a script file that contains SED commands. However, we can use both forms together multiple times. SED provides various command-line options to control its behavior.

Let us see how we can specify multiple SED commands. SED provides the delete command to delete certain lines. Let us delete the 1st, 2nd, and 5th lines. For the time being, ignore all the details of the delete command. We will discuss more about the delete command later.

First, display the file contents using the cat command.

On executing the above code, you get the following result:

Now instruct SED to remove only certain lines. Here, to delete three lines, we have specified three separate commands with -e option.

On executing the above code, you get the following result:

Additionally, we can write multiple SED commands in a text file and provide the text file as an argument to SED. SED can apply each command on the pattern buffer. The following example illustrates the second form of SED.

First, create a text file containing SED commands. For easy understanding, let us use the same SED commands.

On executing the above code, you get the following result:

Now instruct the SED to read commands from the text file. Here, we achieve the same result as shown in the above example.

On executing the above code, you get the following result:

<h2>Standard Options</h2>

SED supports the following standard options:

-n: Default printing of pattern buffer. For example, the following SED command does not show any output:

-e <cmd> : Next argument is an editing command. Here, angular brackets imply mandatory parameter. By using this option, we can specify multiple commands. Let us print each line twice:

On executing the above code, you get the following result:

-f <filename> : Next argument is a file containing editing commands. The angular brackets imply mandatory parameter. In the following example, we specify print command through file:

On executing the above code, you get the following result:

<h2>GNU Specific Options</h2>

Let us quickly go through the GNU specific SED options. Note that these options are GNU specific; and may not be supported by other variants of the SED. In later sections, we will discuss these options in more details.

-n, --quiet, --silent: Same as standard -n option.

-e script, --expression=script: Same as standard -e option.

-f script-file, --file=script-file: Same as standard -f option.

--follow-symlinks: If this option is provided, the SED follows symbolic links while editing files in place.

-i[SUFFIX], --in-place[=SUFFIX]: This option is used to edit file in place. If suffix is provided, it takes a backup of the original file, otherwise it overwrites the original file.

-l N, --line-lenght=N: This option sets the line length for l command to N characters.

--posix: This option disables all GNU extensions.

-r, --regexp-extended: This option allows to use extended regular expressions rather than basic regular expressions.

-u, --unbuffered: When this option is provided, the SED loads minimal amount of data from the input files and flushes the output buffers more often. It is useful for editing the output of "tail -f" when you do not want to wait for the output.

-z, --null-data: By default, the SED separates each line by a new-line character. If NULL-data option is provided, it separates the lines by NULL characters.

sed [-n] [-e] 'command(s)' files

sed [-n] -f scriptfile files

</pre>

First, display the file contents using the cat command.

[jerry]$ cat books.txt

</pre>

On executing the above code, you get the following result:

1) A Storm of Swords, George R. R. Martin, 1216

2) The Two Towers, J. R. R. Tolkien, 352

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho, 288

6) A Game of Thrones, George R. R. Martin, 864

</pre>

Now instruct SED to remove only certain lines. Here, to delete three lines, we have specified three separate commands with -e option.

[jerry]$ sed -e '1d' -e '2d' -e '5d' books.txt

</pre>

On executing the above code, you get the following result:

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

6) A Game of Thrones, George R. R. Martin, 864

</pre>

First, create a text file containing SED commands. For easy understanding, let us use the same SED commands.

[jerry]$ echo -e "1d\n2d\n5d" > commands.txt

[jerry]$ cat commands.txt

</pre>

On executing the above code, you get the following result:

</pre>

Now instruct the SED to read commands from the text file. Here, we achieve the same result as shown in the above example.

[jerry]$ sed -f commands.txt books.txt

</pre>

On executing the above code, you get the following result:

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

6) A Game of Thrones,George R. R. Martin, 864

</pre>

<h2>Standard Options</h2>

SED supports the following standard options:

<li>-n: Default printing of pattern buffer. For example, the following SED command does not show any output:</li>

[jerry]$ sed -n '' quote.txt

</pre>

<li>-e <cmd> : Next argument is an editing command. Here, angular brackets imply mandatory parameter. By using this option, we can specify multiple commands. Let us print each line twice:</li>

[jerry]$ sed -e '' -e 'p' quote.txt

</pre>

</ul>

On executing the above code, you get the following result:

There is only one thing that makes a dream impossible to achieve: the fear of failure.

- Paulo Coelho, The Alchemist

</pre>

<li>-f <filename> : Next argument is a file containing editing commands. The angular brackets imply mandatory parameter. In the following example, we specify print command through file:</li>

</ul>

[jerry]$ echo "p" > commands

[jerry]$ sed -n -f commands quote.txt

</pre>

On executing the above code, you get the following result:

There is only one thing that makes a dream impossible to achieve: the fear of failure.

- Paulo Coelho, The Alchemist

</pre>

<title>Stream Editor - Loops</title>

<h1>Stream Editor - Loops</h1>

Like other programming languages, SED too provides a looping and branching facility to control the flow of execution. In this chapter, we are going to explore more about how to use loops and branches in SED.

A loop in SED works similar to a goto statement. SED can jump to the line marked by the label and continue executing the remaining commands. In SED, we can define a label as follows:

In the above example, a name after colon(:) implies the label name.

To jump to a specific label, we can use the b command followed by the label name. If the label name is omitted, then the SED jumps to the end of the SED file.

Let us write a simple SED script to understand the loops and branches. In our books.txt file, there are several entries of book titles and their authors. The following example combines a book title and its author name in one line separated by a comma. Then it searches for the pattern "Paulo". If the pattern matches, it prints a hyphen(-) in front of the line, otherwise it jumps to the Print label which prints the line.

On executing the above code, you get the following result:

At first glance, the above script may look cryptic. Let us demystify this.

The first two commands are self-explanatory h;n;H;x and s/\n/, / combine the book title and its author separated by a comma(,).

The third command jumps to the label Print only when the pattern does not match, otherwise substitution is performed by the fourth command.

:Print is just a label name and as you already know, p is the print command.

To improve readability, each SED command is placed on a separate line. However, one can choose to place all the commands in one line as follows:

On executing the above code, you get the following result:

:label

:start

:end

:up

</pre>

In the above example, a name after colon(:) implies the label name.

To jump to a specific label, we can use the b command followed by the label name. If the label name is omitted, then the SED jumps to the end of the SED file.

[jerry]$ sed -n '

h;n;H;x

s/\n/, /

/Paulo/!b Print

s/^/- /

:Print

p' books.txt

</pre>

On executing the above code, you get the following result:

A Storm of Swords, George R. R. Martin

The Two Towers, J. R. R. Tolkien

- The Alchemist, Paulo Coelho

The Fellowship of the Ring, J. R. R. Tolkien

- The Pilgrimage, Paulo Coelho

</pre>

A Game of Thrones, George R. R. Martin

</pre>

At first glance, the above script may look cryptic. Let us demystify this.

<li>The first two commands are self-explanatory h;n;H;x and s/\n/, / combine the book title and its author separated by a comma(,).</li>

<li>The third command jumps to the label Print only when the pattern does not match, otherwise substitution is performed by the fourth command.</li>

<li>:Print is just a label name and as you already know, p is the print command.</li>

</ul>

To improve readability, each SED command is placed on a separate line. However, one can choose to place all the commands in one line as follows:

[jerry]$ sed -n 'h;n;H;x;s/\n/, /;/Paulo/!b Print; s/^/- /; :Print;p' books.txt

</pre>

On executing the above code, you get the following result:

A Storm of Swords, George R. R. Martin

The Two Towers, J. R. R. Tolkien

- The Alchemist, Paulo Coelho

The Fellowship of the Ring, J. R. R. Tolkien

- The Pilgrimage, Paulo Coelho

A Game of Thrones, George R. R. Martin

</pre>

<title>Stream Editor - Branches</title>

<h1>Stream Editor - Branches</h1>

Branches can be created using the t command. The t command jumps to the label only if the previous substitute command was successful. Let us take the same example as in the previous chapter, but instead of printing a single hyphen(-), now we print four hyphens. The following example illustrates the usage of the t command.

When the above code is executed, it will produce the following result.

In the above example, the first two commands are self-explanatory. The third command defines a label Loop. The fourth command prepends hyphen(-) if the line contains the string "Paulo" and the t command repeats the procedure until there are four hyphens at the beginning of the line.

To improve readability, each SED command is written on a separate line. Otherwise, we can write a one-liner SED as follows:

When the above code is executed, it will produce the following result.

[jerry]$ sed -n '

h;n;H;x

s/\n/, /

:Loop

/Paulo/s/^/-/

/----/!t Loop

p' books.txt

</pre>

When the above code is executed, it will produce the following result.

A Storm of Swords, George R. R. Martin

The Two Towers, J. R. R. Tolkien

----The Alchemist, Paulo Coelho

The Fellowship of the Ring, J. R. R. Tolkien

----The Pilgrimage, Paulo Coelho

A Game of Thrones, George R. R. Martin

</pre>

To improve readability, each SED command is written on a separate line. Otherwise, we can write a one-liner SED as follows:

[jerry]$ sed -n 'h;n;H;x; s/\n/, /; :Loop;/Paulo/s/^/-/; /----/!t Loop; p' books.txt

</pre>

When the above code is executed, it will produce the following result.

A Storm of Swords, George R. R. Martin

The Two Towers, J. R. R. Tolkien

----The Alchemist, Paulo Coelho

The Fellowship of the Ring, J. R. R. Tolkien

----The Pilgrimage, Paulo Coelho

A Game of Thrones, George R. R. Martin

</pre>

<title>Stream Editor - Pattern Buffer</title>

<h1>Stream Editor - Pattern Buffer</h1>

One of the basic operations we perform on any file is display its contents. For this purpose, we can use the print command which prints the contents of the pattern buffer. So let us learn more about the pattern buffer

First create a file containing the line number, the name of the book, its author, and the number of pages. In this tutorial, we will be using this file. You can use any text file according to your convenience. Our text file will look like this:

Now, let us print the file contents.

When the above code is executed, it will produce the following result.

You might wonder why each line is being displayed twice. Let us find out.

Do you remember the workflow of SED? By default, SED prints the contents of the pattern buffer. In addition, we have included a print command explicitly in our command section. Hence each line is printed twice. But don't worry. SED has the -n option to suppress the default printing of the pattern buffer. The following command illustrates that.

When the above code is executed, it will produce the following result.

Congratulations! we got the expected result. By default, SED operates on all lines. But we can force SED to operate only on certain lines. For instance, in the example below, SED only operates on the 3rd line. In this example, we have specified an address range before the SED command.

When the above code is executed, it will produce the following result.

Additionally, we can also instruct SED to print only certain lines. For instance, the following code prints all the lines from 2 to 5. Here we have used the comma(,) operator to specify the address range.

When the above code is executed, it will produce the following result.

There is also a special character Dollar($) which represents the last line of the file. So let us print the last line of the file.

When the above code is executed, it will produce the following result.

However we can also use Dollar($) character to specify address range. Below example prints through line 3 to last line.

When the above code is executed, it will produce the following result.

We learnt how to specify an address range using the comma(,) operator. SED supports two more operators that can be used to specify address range. First is the plus(+) operator and it can be used with the comma(,) operator. For instance M, +n will print the next n lines starting from line number M. Sounds confusing? Let us check it with a simple example. The following example prints the next 4 lines starting from line number 2.

When the above code is executed, it will produce the following result.

Optionally, we can also specify address range using the tilde(~) operator. It uses M~n form. It indicates that SED should start at line number M and process every n(th) line. For instance, 50~5 matches line number 50, 55, 60, 65, and so on. Let us print only odd lines from the file.

When the above code is executed, it will produce the following result.

The following code prints only even lines from the file.

When the above code is executed, it will produce the following result.

[jerry]$ vi books.txt

1) A Storm of Swords, George R. R. Martin, 1216

2) The Two Towers, J. R. R. Tolkien, 352

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho,288

6) A Game of Thrones, George R. R. Martin, 864

</pre>

Now, let us print the file contents.

[jerry]$ sed 'p' books.txt

</pre>

When the above code is executed, it will produce the following result.

1) A Storm of Swords, George R. R. Martin, 1216

2) The Two Towers, J. R. R. Tolkien, 352

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho, 288

6) A Game of Thrones, George R. R. Martin, 864

</pre>

You might wonder why each line is being displayed twice. Let us find out.

[jerry]$ sed -n 'p' books.txt

</pre>

When the above code is executed, it will produce the following result.

1) A Storm of Swords, George R. R. Martin, 1216

2) The Two Towers, J. R. R. Tolkien, 352

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho, 288

6) A Game of Thrones, George R. R. Martin, 864

</pre>

[jerry]$ sed -n '3p' books.txt

</pre>

When the above code is executed, it will produce the following result.

3) The Alchemist, Paulo Coelho, 197

</pre>

[jerry]$ sed -n '2,5 p' books.txt

</pre>

When the above code is executed, it will produce the following result.

2) The Two Towers, J. R. R. Tolkien, 352

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho, 288

</pre>

There is also a special character Dollar($) which represents the last line of the file. So let us print the last line of the file.

[jerry]$ sed -n '$ p' books.txt

</pre>

When the above code is executed, it will produce the following result.

6) A Game of Thrones, George R. R. Martin, 864

</pre>

However we can also use Dollar($) character to specify address range. Below example prints through line 3 to last line.

[jerry]$ sed -n '3,$ p' books.txt

</pre>

When the above code is executed, it will produce the following result.

3) The Alchemist, Paulo Coelho, 197 4) The Fellowship of the Ring, J. R. R. Tolkien, 432 5) The Pilgrimage, Paulo Coelho, 288 6) A Game of Thrones, George R. R. Martin, 864

</pre>

[jerry]$ sed -n '2,+4 p' books.txt

</pre>

When the above code is executed, it will produce the following result.

2) The Two Towers, J. R. R. Tolkien, 352

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho, 288

6) A Game of Thrones, George R. R. Martin, 864

</pre>

[jerry]$ sed -n '1~2 p' books.txt

</pre>

When the above code is executed, it will produce the following result.

1) A Storm of Swords, George R. R. Martin, 1216

3) The Alchemist, Paulo Coelho, 197

5) The Pilgrimage, Paulo Coelho, 288

</pre>

The following code prints only even lines from the file.

[jerry]$ sed -n '2~2 p' books.txt

</pre>

When the above code is executed, it will produce the following result.

2) The Two Towers, J. R. R. Tolkien, 352

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

6) A Game of Thrones, George R. R. Martin, 864

</pre>

<title>Stream Editor - Pattern Range</title>

<h1>Stream Editor - Pattern Range</h1>

In the previous chapter, we learnt how SED handles an address range. This chapter covers how SED takes care of a pattern range. A pattern range can be a simple text or a complex regular expression. Let us take an example. The following example prints all the books of the author Paulo Coelho.

On executing the above code, you get the following result:

In the above example, the SED operates on each line and prints only those lines that match the string Paulo.

We can also combine a pattern range with an address range. The following example prints lines starting with the first match of Alchemist until the fifth line.

On executing the above code, you get the following result:

We can use the Dollar($) character to print all the lines after finding the first occurrence of the pattern. The following example finds the first occurrence of the pattern The and immediately prints the remaining lines from the file

On executing the above code, you get the following result:

We can also specify more than one pattern ranges using the comma(,) operator. The following example prints all the lines that exist between the patterns Two and Pilgrimage.

On executing the above code, you get the following result:

Additionally, we can use the plus(+) operator within a pattern range. The following example finds the first occurrence of the pattern Two and prints the next 4 lines after that.

On executing the above code, you get the following result:

We have supplied here only a few examples to get you acquainted with SED. You can always get to know more by trying a few examples on your own.

[jerry]$ sed -n '/Paulo/ p' books.txt

</pre>

On executing the above code, you get the following result:

3) The Alchemist, Paulo Coelho, 197

5) The Pilgrimage, Paulo Coelho, 288

</pre>

In the above example, the SED operates on each line and prints only those lines that match the string Paulo.

We can also combine a pattern range with an address range. The following example prints lines starting with the first match of Alchemist until the fifth line.

[jerry]$ sed -n '/Alchemist/, 5 p' books.txt

</pre>

On executing the above code, you get the following result:

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho, 288

</pre>

[jerry]$ sed -n '/The/,$ p' books.txt

</pre>

On executing the above code, you get the following result:

2) The Two Towers, J. R. R. Tolkien, 352

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho, 288

6) A Game of Thrones, George R. R. Martin, 864

</pre>

We can also specify more than one pattern ranges using the comma(,) operator. The following example prints all the lines that exist between the patterns Two and Pilgrimage.

[jerry]$ sed -n '/Two/, /Pilgrimage/ p' books.txt

</pre>

On executing the above code, you get the following result:

2) The Two Towers, J. R. R. Tolkien, 352

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho, 288

</pre>

Additionally, we can use the plus(+) operator within a pattern range. The following example finds the first occurrence of the pattern Two and prints the next 4 lines after that.

[jerry]$ sed -n '/Two/, +4 p' books.txt

</pre>

On executing the above code, you get the following result:

2) The Two Towers, J. R. R. Tolkien, 352

3) The Alchemist, Paulo Coelho, 197

4) The Fellowship of the Ring, J. R. R. Tolkien, 432

5) The Pilgrimage, Paulo Coelho, 288

6) A Game of Thrones, George R. R. Martin, 864

</pre>

<title>Stream Editor - Basic Commands</title>

<h1>Stream Editor - Basic Commands</h1>

This chapter describes several useful SED commands.

<h2>Delete Command</h2>

SED provides various commands to manipulate text. Let us first explore about the delete command. Here is how you execute a delete command:

address1 and address2 are the starting and the ending addresses respectively, which can be either line numbers or pattern strings. Both of these addresses are optional parameters.

As the name suggests, the delete command is used to perform delete operation and since the SED operates on line, we can say that this command is used to delete lines. Note that the delete command removes lines only from the pattern buffer; the line is not sent to the output stream and the original file remains unchanged. The following example illustrates the point.

But where is the output? If no line address is provided, then the SED operates on every line by default. Hence, it deletes all the lines from the pattern buffer. That is why the command does not print anything on the standard output.

Let us instruct the SED to operate only on certain lines. The following example removes the 4th line only.

On executing the above code, you get the following result:

Additionally, SED also accepts address range using comma(,). We can instruct the SED to remove N1 to N2 lines. For instance, the following example deletes all the lines from 2 through 4.

On executing the above code, you get the following result:

SED's address range is not only limited to numbers. We can also specify patterns as an address. The following example removes all the books of the author Paulo Coelho.

On executing the above code, you get the following result:

We can also specify an address range using textual pattern. The following example removes all lines between the patterns Storm and Fellowship.

In addition to this, we can also use dollar($), plus(+), and tilde(~) operators with SED.

<h2>Write Command</h2>

One of the important operations we perform on any file is backup, i.e., we make another copy of the file. SED provides the write command to store the contents of the pattern buffer in a file. Given below is the syntax of the write command which is similar to the delete command.

Here, address1 and address2 are the starting and the ending address respectively, which can be either line numbers or pattern strings. Both of these addresses are optional parameters.

In the above syntax, w refers to the write command and file is the file name in which you store contents. Be careful with the file parameter. When a file name is provided, the SED creates a file on the fly if it is not present, and overwrites it if it is already present.

Let us make an exact copy of the file using SED. Note that there must be exactly one space between w and file.

We created another file called books.bak. Now verify that both the files have identical content.

On executing the above code, you get the following result:

You may assume that the cp command does exactly the same thing. Yes! The cp command does the same thing, but SED is a matured utility. It allows creating a file containing only certain lines from the source file. Let us store only even lines to another file.

On executing the above code, you get the following result:

You can also use comma(,), dollar($), and plus(+) operators with the write command.

In addition to this, SED also supports pattern matching with the write command. Suppose you want to store all the books of individual authors into a separate file. One boring and lengthy way is do it manually, and the smarter way is to use SED.

In the above example, we are matching each line against a pattern and storing the matched line in a particular file. It is very simple. To specify multiple commands, we used -e switch of the SED command. Now let use see what each file contains:

On executing the above code, you get the following result:

Let us display the file contents.

On executing the above code, you get the following result:

Let us display the file contents.

On executing the above code, you get the following result:

Excellent! We got the expected result. SED is really an amazing utility.

<h2>Append Command</h2>

One of the most useful operations of any text editor is to provide append functionality. SED supports this operation through its append command. Given below is the syntax of append:

Let us append a new book entry after line number 4. The following example shows how to do it

On executing the above code, you get the following result:

In the command section, 4 implies the line number, a is the append command, and the remaining part is the text to be appended.

Let us insert a text line at the end of the file. To do this, use $ as the address. The following example illustrates this:

On executing the above code, you get the following result:

Apart from line number, we can also specify an address using textual pattern. For instance, the following example appends text after matching the string The Alchemist.

On executing the above code, you get the following result:

Note that if there are multiple patterns matching, then the text is appended after each match. The following example illustrates this scenario.

On executing the above code, you get the following result:

<h2>Change Command</h2>

SED provides change or replace command which is represented by c. This command helps replace an existing line with new text. When line range is provided, all the lines are replaced as a group by a single text line. Given below is the syntax of the change command:

Let us replace the third line with some other text.

On executing the above code, you get the following result:

SED also accepts patterns as an address. In the following example, a line is replaced when the pattern match succeeds.

SED also allows replacement of multiple lines with a single line. The following example removes lines from fourth through sixth and replaces them with new text.

On executing the above code, you get the following result:

<h2>Insert Command</h2>

The insert command works much in the same way as append does. The only difference is that it inserts a line before a specific position. Given below is the syntax of the insert command:

Let us understand the insert command with some examples. The following command inserts a new entry before the fourth line.

On executing the above code, you get the following result:

In the above example, 4 is the location number, i implies the insert command, and the remaining part is the text to be inserted.

To insert text at the start of a file, provide the line address as 1. The following command illustrates this:

On executing the above code, you get the following result:

Additionally, we can insert multiple lines. The following command inserts two lines before the last line.

On executing the above code, you get the following result:

Note that the entries to be inserted are entered on separate lines and delimited by the backslash(\) character.

<h2>Translate Command</h2>

SED provides a command to translate characters and it is represented as y. It transforms the characters by position. Given below is the syntax of the translate command:

Note that translation is based on the position of the character from list 1 to the character in the same position in list 2 and both lists must be explicit character lists. Regular expressions and character classes are unsupported. Additionally, the size of list 1 and list 2 must be same.

The following example converts Arabic numbers to Roman numbers.

On executing the above code, you get the following result:

<h2>l command</h2>

Can you differentiate between words separated by spaces and words separated by tab characters only by looking at them? Certainly not. But SED can do this for you. SED uses the l command to display hidden characters in the text. For example, tab character with \t and End-Of-Line with $ character. Given below is the syntax of the l command.

Let us create a file with tab characters for demonstration. For simplicity, we are going to use the same file, just by replacing spaces with tabs. Wait! But how to do that — by opening the file in a text editor and replacing each space with tab? Certainly not! We can make use of SED commands for that.

Now let us display the hidden characters by using the l command:

On executing the above code, you get the following result:

Like other SED commands, it also accepts line numbers and patterns as an address. You can try it yourselves.

Let us take a close look at another interesting feature of SED. We can instruct the SED to perform line wrapping after a certain number of characters. The following example wraps lines after 25 characters.

On executing the above code, you get the following result:

Note that in the above example, wrap limit is provided after l command. In this case, it is 25 characters. This option is GNU specific and may not work with other variants of the SED.

A wrap limit of 0 means never break the line unless there is a new line character. The following simple command illustrates this.

On executing the above code, you get the following result:

<h2>Quit Command</h2>

Quit command instructs the SED to quit the current execution flow. It is represented by the q command. Given below is the syntax of the quit command:

Note that the quit command does not accept range of addresses, it only supports a single address. By default, SED follows read, execute, and repeat workflow; but when the quit command is encountered, it simply stops the current execution.

Let us print the first 3 lines from the file.

On executing the above code, you get the following result:

In addition to line number, we can also use textual patterns. The following command quits when pattern match succeeds.

On executing the above code, you get the following result:

In addition to this, SED can also accept a value which can be used as the exit status. The following command shows its exit status as 100.

On executing the above code, you get the following result:

Now let us verify the exit status.

On executing the above code, you get the following result:

<h2>Read Command</h2>

We can instruct the SED to read the contents of a file and display them when a specific condition matches. The command is represented by the alphabet r. Given below is the syntax of the read command.

Note that there must be exactly one space between the r command and the file name.

Let us understand it with a simple example. Create a sample file called junk.txt.

The following command instructs the SED to read the contents of junk.txt and insert them after the third line.

On executing the above code, you get the following result:

In the above example, 3 implies the line address, r is the command name, and junk.txt is the file name the contents of which are to be displayed. Additionally, the GNU SED also accepts a range of addresses. For instance, the following command inserts the contents of junk.txt after the third, fourth, and fifth lines.

On executing the above code, you get the following result:

Like other SED commands, the read command also accepts pattern as an address. For instance, the following command inserts the contents of junk.txt when the pattern match succeeds.

On executing the above code, you get the following result:

<h2>Execute Command</h2>

We can execute external commands from SED using the execute command. It is represented by e. Given below is the syntax of the execute command.

Let us illustrate the execute command with a simple example. The following SED command executes the UNIX date command before the third line.

On executing the above code, you get the following result:

Like other commands, it also accepts patterns as an address. For example, the following example executes date command when a pattern match succeeds. Note that after each pattern match, first the command is executed and then the contents of the pattern buffer are displayed.

On executing the above code, you get the following result:

If you observe the syntax of the e command carefully, you will notice that command is optional. When no command is provided after e, it treats the contents of the pattern buffer as an external command. To illustrate this, let us create a commands.txt file with a few simple commands.

On executing the above code, you get the following result:

Commands from the file are self-explanatory. In the absence of command after e, SED executes all these commands one by one. The following simple example illustrates this.

On executing the above code, you get the following result:

Like other SED commands, the execute command also accepts all valid ranges of addresses.

<h2>Miscellaneous Commands</h2>

By default, SED operates on single line, however it can operate on multiple lines as well. Multi-line commands are denoted by uppercase letters. For example, unlike the n command, the N command does not clear and print the pattern space. Instead, it adds a newline (\n) at the end of the current pattern space and appends the next line from the input-file to the current pattern space and continues with the SED's standard flow by executing the rest of the SED commands. Given below is the syntax of the N command.

Let us print a comma-separated list of book titles and their respective authors. The following example illustrates this.

On executing the above code, you get the following result:

Let us understand how the above example works. The N command reads the first line, i.e.,A Storm of Swords into the pattern buffer and appends \n followed by the next line. The pattern space now contains A Storm of Swords\nGeorge R. R. Martin. In the next step, we are replacing the newline with a comma.

Like p command, we have a P command to print the first part (up to embedded newline) of the multi-line pattern space created by the N command. Given below is the syntax of the P command which is similar to the p command.

In the previous example, we saw that the N command creates a newline- separated list of book titles and their authors. Let us print only the first part of it, i.e., only the titles of the book. The following command illustrates this.

On executing the above code, you get the following result:

Note that in the absence of N, it behaves same as the p command. The following simple command illustrates this scenario.

On executing the above code, you get the following result:

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