Son Nguyen's blog

Source: http://www.thegeekstuff.com/

Let us review how to print file lines using address and patterns in this first part of sed tutorial.

We’ll be posting several awesome sed tutorials with examples in the upcoming weeks.

Unix Sed Introduction

sed is a “non-interactive” stream-oriented editor. Since its an “non-interactive” it can be used to automate editing if desired.
The name sed is an abbreviation for stream editor, and the utility derives many of its commands from the ed line-editor (ed was the first UNIX text editor).
This allows you to edit multiple files, or to perform common editing operations without ever having to open vi or emacs.
sed reads from a file or from its standard input, and outputs to its standard output.
sed has two buffers which are called pattern buffer and hold buffer. Both are initially empty.

Unix Sed Working methodology

This is called as one execution cycle. Cycle continues till end of file/input is reached.

Read a entire line from stdin/file.
Removes any trailing newline.
Places the line, in its pattern buffer.
Modify the pattern buffer according to the supplied commands.
Print the pattern buffer to stdout.

Printing Operation in Sed

Linux Sed command allows you to print only specific lines based on the line number or pattern matches. “p” is a command for printing the data from the pattern buffer.

To suppress automatic printing of pattern space use -n command with sed. sed -n option will not print anything, unless an explicit request to print is found.

Syntax:
# sed -n 'ADDRESS'p filename

# sed -n '/PATTERN/p' filename

Let us first create thegeekstuff.txt file that will be used in all the examples mentioned below.

# cat thegeekstuff.txt
1. Linux - Sysadmin, Scripting etc.
2. Databases - Oracle, mySQL etc.
3. Hardware
4. Security (Firewall, Network, Online Security etc)
5. Storage
6. Cool gadgets and websites
7. Productivity (Too many technologies to explore, not much time available)
8. Website Design
9. Software Development
10.Windows- Sysadmin, reboot etc.

5 Sed ADDRESS Format Examples

Sed Address Format 1: NUMBER

This will match only Nth line in the input.

# sed -n ‘N’p filename

For example, 3p prints third line of input file thegeekstuff.txt as shown below.

# sed -n '3'p thegeekstuff.txt
3. Hardware

Sed Address Format 2: NUMBER1~NUMBER2

M~N with “p” command prints every Nth line starting from line M.

# sed -n ‘M~N’p filename

For example, 3~2p prints every 2nd line starting from 3rd line as shown below.

# sed -n '3~2'p thegeekstuff.txt
3. Hardware
5. Storage
7. Productivity (Too many technologies to explore, not much time available)
9. Software Development

Sed Address Format 3: START,END

M,N with “p” command prints Mth line to Nth line.

# sed -n ‘M,N’p filename

For example, 4,8p prints from 4th line to 8th line from input file thegeekstuff.txt

# sed -n '4,8'p thegeekstuff.txt
4. Security (Firewall, Network, Online Security etc)
5. Storage
6. Cool gadgets and websites
7. Productivity (Too many technologies to explore, not much time available)
8. Website Design

Sed Address Format 4: ‘$’ Last Line

$ with “p” command matches only the last line from the input.

# sed -n ‘$’p filename

For example, $p prints only the last line as shown below.

# sed -n '$'p thegeekstuff.txt
10.Windows- Sysadmin, reboot etc.

Sed Address Format 5: NUMBER,$

N,$ with “p” command prints from Nth line to end of file.

# sed -n ‘N,$p’ filename

For example 4,$p prints from 4th line to end of file.

# sed -n '4,$p' thegeekstuff.txt
4. Security (Firewall, Network, Online Security etc)
5. Storage
6. Cool gadgets and websites
7. Productivity (Too many technologies to explore, not much time available)
8. Website Design
9. Software Development
10.Windows- Sysadmin, reboot etc.

6 Sed PATTERN Format Examples

Sed Pattern Format 1: PATTERN

PATTERN could be unix regular expression. The below command prints only the line which matches the given pattern.

# sed -n /PATTERN/p filename

For example, following prints the line only which matches the pattern “Sysadmin”.

# sed -n /Sysadmin/p thegeekstuff.txt
1. Linux - Sysadmin, Scripting etc.
10.Windows- Sysadmin, reboot etc.

Sed Pattern Format 2: /PATTERN/,ADDRESS

# sed -n ‘/PATTERN/,Np’ filename

For example, following prints lines which matches the pattern to Nth line, from input. 3rd line matches the pattern “Hardware”, so it prints from 3rd line to 6th line.

# sed -n '/Hardware/,6p' thegeekstuff.txt
3. Hardware
4. Security (Firewall, Network, Online Security etc)
5. Storage
6. Cool gadgets and websites

Sed Pattern Format 3: ADDRESS,/PATTERN/

It prints from the Nth line of the input, to the line which matches the pattern. If the pattern doesnt match, it prints upto end of the input.

# sed -n ‘N,/PATTERN/p’ filename

For example, 4th line matches the pattern “Security”, so it prints from 3rd line to 4th line.

# sed -n '3,/Security/p' thegeekstuff.txt
3. Hardware
4. Security (Firewall, Network, Online Security etc)

Sed Pattern Format 4: /PATTERN/,$

It prints from the line matches the given pattern to end of file.

# sed -n ‘/PATTERN/,$p’ filename

# sed -n '/Website/,$p' thegeekstuff.txt
8. Website Design
9. Software Development
10.Windows- Sysadmin, reboot etc.

Sed Pattern Format 5: /PATTERN/,+N

It prints the lines which matches the pattern and next N lines following the matched line.

# sed -n ‘/PATTERN/,+Np’ filename

For example, following prints the 5th line which matches the pattern /Storage/ and next two lines following /Storage/.

# sed -n '/Storage/,+2p' thegeekstuff.txt
5. Storage
6. Cool gadgets and websites
7. Productivity (Too many technologies to explore, not much time available)

Sed Pattern Format 6: /PATTERN/,/PATTERN/

Prints the section of file between two regular expression (including the matched line ).

# sed -n ‘/P1/,/P2/p’ filename

For example, 5th line matches “Storage” and 8th line matches “Design”, so it prints 5th to 8th.

# sed -n '/Storage/,/Design/p' thegeekstuff.txt
5. Storage
6. Cool gadgets and websites
7. Productivity (Too many technologies to explore, not much time available)
8. Website Design

Today, when I was installing some missing Perl modules for SpamAssassin on a bare Ubuntu 8.04 LTS Hardy Heron installation I had to use the CPAN shell for a few of those modules. But when I tried to install the first of the Perl modules not available via apt, IP::Country::Fast, I got the following output:

Warning: prerequisite Geography::Countries  not found.
Writing Makefile for IP::Country
    -- NOT OK
Running make test
  Can't test without successful make
Running make install
  make had returned bad status, install seems impossible

At first I thought this had to do with the Perl module Geography::Countries not being installed as well, so I tried to install that one via the CPAN shell. But alas, this also resulted in the "NOT OK" message:

Writing Makefile for Geography::Countries
    -- NOT OK
Running make test
  Can't test without successful make
Running make install
  make had returned bad status, install seems impossible

After some thinking I realised that I was working on a bare Ubuntu installation and make might be missing... And since I had used the default configuration of CPAN instead of manual configuration the first time I started the CPAN shell using perl -MCPAN -e shell I overlooked this. On the other hand the "NOT OK" warning CPAN gives is extremely unclear.

Anyway, I left the CPAN shell and used apt-get install make to install make. Next I used which make to obtain the path to make, since I had to configure this into the CPAN shell.

Back into the CPAN shell I first verified the current setting of the make option using o conf make:

cpan> o conf make
    make

The above might be read as "the current value of make is make" but it actually shows the name of the option, make, followed by its value, which is empty.

After I set the value of make to the path of make and commited this change, see commands and output below, I was able to install the required Perl modules.

cpan> o conf make /usr/bin/make
    make               /usr/bin/make

cpan> o conf commit
commit: wrote /etc/perl/CPAN/Config.pm

Well... until I had to install a module that required a C++ compiler.