UNIX SED Introduction

· Sed is a “non-interactive” stream-oriented editor. Since its an “non-interactive” it can be used to automate editing.

· This allows you to edit multiple files, or to perform common editing operations without opening 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 Method

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

1. Read a entire line from stdin/file.

2. Removes any trailing newline.

3. Places the line, in its pattern buffer.

4. Modify the pattern buffer according to the supplied commands

5. 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.

Syntax:

# sed -n ‘ADDRESS’p filename

# sed -n ‘/PATTERN/p’ filename

Create the txt file sample.txt that will be used in all examples below.

# cat sample.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)

8. Website Design

9. Software Development

10.Windows- Sysadmin, reboot etc.

Sed Address Format 1: NUMBER

This will only match Nth line in the input.

#sed –n ‘N’p filename

For example, 3p prints 3^rd line of the input file sample.txt as 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)

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)

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)

8. Website Design

9. Software Development

10.Windows- Sysadmin, reboot etc.

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)

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)

8. Website Design

Delete File Lines Using Address and pattern in Sed

“p” command prints the buffer (Remember to use “-n” option with “p”)

“d” command is just opposite, it’s for deletion. “d” will delete the pattern space buffer and immediately starts the next cycle.

Syntax:

# sed ‘ADDRESS’d filename

# sed /PATTERN/d filename

Delete the Nth line.

“Nd” delete the Nth line and prints the other lines.

For example, 3d deletes 3^rd line and prints other lines.

$sed 3d sample.txt

Delete Starting from 3^rd line and every 2^nd line from there.

$sed ‘3~2d’ sample.txt

Delete from 4ht to 8^th line from file

$sed ‘4,8d’ sample.txt

Delete the last line from input

$sed ‘$d’ sample.txt

Delete the line which matches the given pattern from input

$sed /Sysadmin/d sample.txt

Delete the line from which matches the given pattern to end of the file

$sed ‘/Website/ ,$d’ sample.txt

Delete the line from which matches the given pattern and 2 lines next to that

$sed ‘Storage/ ,+2d’ sample.txt

Delete blank line from a file using sed.

$sed ‘/^$/d’ sample.txt

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