Difference between revisions of "Sed-Stream-Editor/C2/Sed-special-characters/English"

Learning Objectives

• Print command

Also, how to use special characters such as

• $ (dollar)
• ^ (caret)
• = (equal to)
• &(ampersand)

in Sed command.

System requirements

Prerequisites

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Code files – IndianBooks.txt

• The files used in this tutorial are available in the Code Files link on this tutorial page.
• Please download and extract them
• Make a copy and then use them while practicing

Press the Enter key after every command.

> cat IndianBooks

Type cat space IndianBooks.txt

In this tutorial, I’ll be using this file for demonstration.

Highlight p

sed space within single quotes p space IndianBooks.txt

'p' is the command for printing the data from the pattern buffer.

In the output, we can see that each line is displayed twice.

Recall the workflow of Sed.

By default, Sed prints the content of the pattern buffer.

We have included the print option 'p' in the above command. So it prints twice.

Highlight -n

Type the command with -n as shown.

-n (hyphen n) is the Sed command line flag.

> sed -n ‘5p’ IndianBooks.txt

Highlight 5p

Type the command as shown.

5p prints the fifth line of the input file IndianBooks.txt

Highlight 3,6p

Here we have specified an address range in the Sed command.

This will print from the 3rd line to the 6th line .

Highlight $

Type the command as shown.

This command prints from the 4th line to the last line.

> sed -n ‘3, +3p’ IndianBooks.txt

Type the command with plus(+) operator as shown.

This command prints the next 3 lines starting from the third line.

> sed -n ‘1~2p’ IndianBooks.txt

For example, this command prints the odd line numbers from the file.

That is, it starts from line number 1 and processes every second line.

>sed -n ‘ /Gandhi/ p’ IndianBooks.txt

Highlight between forward slash

Type sed space hyphen n space within single quotes forward slash Gandhi forward slash p space IndianBooks.txt

Note that pattern has to be specified within forward slashes.

Sed operates on each line and prints only those lines that match the string Gandhi.

Highlight ! operator

We can print the lines that don’t contain the word Gandhi.

Use negation operator as shown here and see the output.

^ Matches the beginning of the line

$ Matches the end of the line

. Matches any single character

• Matches zero or more occurrences

[ ] Matches all the characters inside the [ ]

Caret matches the beginning of the line

Dollar matches the end of the line

Dot matches any single character

Asterisk matches zero or more occurrences

Square brackets matches all the characters inside it

> sed -n ‘/^1/ p’ IndianBooks.txt

This command prints all the lines that starts with the pattern ‘1’ (one).

The caret(^) symbol matches the start of a line.

>sed -n ‘/3$/ p’ IndianBooks.txt

This command prints all the lines that end with the pattern ‘3’.

>sed -n ‘/...8$/ p’ IndianBooks.txt

Dot matches any single character.

This command prints all the four letter text that ends with 8.

>sed -n '/Ind*/ p' IndianBooks.txt

Asterisks (*) matches the zero or more occurrence of the preceding character.

This prints the line that matches "India", "Indira" and so on.

Highlight =

Equal to command is used to print line numbers in standard output.

We can see the line number followed by the content.

This prints the line numbers for the first 5 lines and the remaining without the line numbers.

Type the command as shown.

This prints only the line numbers of the line that has the pattern ‘My’

Type the command as shown and see the output.

sed 's/^.*/(&)/' IndianBooks.txt

sed 's/^.*dhi/(&)/' IndianBooks.txt

Type the command.

When ampersand is used in the search string, it replaces with whatever text matches the original string.

This command inserts parentheses in all the lines.

Let’s see another example.

This command puts parentheses around the matched text which ends with ‘dhi’.

[] regular expression:

Character class Description

[:alnum:] Alphanumeric [a-z A-Z 0-9]

[:alpha:] Alphabetic [a-z A-Z]

[:blank:] Spaces or tabs

[:digit:] Numeric digits [0-9]

[:lower:] Lower-case [a-z]

[:space:] Whitespace

[:upper:] Upper-case [A-Z]

Let us see a few examples on how to use these in regular expression.

Highlight the output

Type the command as shown.

In regular expression terminology, a character set is represented by square brackets.

This command matches the pattern "Truth" with capital T and small ‘t’.

Then it replaces the word with TRUTH, all in capital letters.

sed 's/19[0-9]*/****/' IndianBooks.txt

Highlight 19[0-9]

Highlight ****

Highlight the output

Type the command as shown.

Note this regular expression.

It should match with the string starting with nineteen and any character within the range 0 to 9.

Then it is replaced with 4 asterisks.

In the output, we can see all the published years are replaced with 4 asterisks.

Highlight s

Highlight the output

Here, the digit represents number 0 to 9 as the search pattern.

This command adds the text ‘Book No’ at the beginning of each line.

Highlight year

> sed ‘s/digit:*$/Published on: &/’ IndianBooks.txt

Highlight digit:*$

In IndianBooks.txt , the last entry is the published year.

Let us add the word “Published on” before the year.

Type the command as shown.

This command finds the last occurrence of the digit and replaces with ‘Published on:’

Slide 8:

Summary

• Print command
• special characters such as
• $ (dollar)
• ^ (caret)
• = (equal to)
• &(ampersand)

in Sed command.

Assignment

1. sed 's/Indi.*/****/' IndianBooks.txt
2. sed 's/Indi[a-z]*a/****/' IndianBooks.txt

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