Difference between revisions of "Sed-Stream-Editor/C2/Sed-commands-with-Files/English"

Learning Objectives

• Delete command
• Write command
• Read command
• Append command
• Insert command
• Change command
• Execute command

System requirements

Prerequisites

If not, then go through the relevant spoken tutorials on this website.

Delete Command

• Sed command can be used to remove specific lines which matches a given pattern in the file.
• This command removes lines only from the pattern buffer.
• The original file remains unchanged.

Syntax: sed [range1][range2]d filename Highlight according to narration

• range1, range2 are the starting and ending range.
• It can be either a line number or pattern strings.
• d specifies the delete option

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 practising

Press the Enter key after every command.

I’ll be using this file for demonstration of various file commands.

> sed ‘d’ IndianBooks.txt

Type the command as shown.

We couldn’t see any output. Why?

We didn’t give any line address. So Sed operates on every line by default.

It deletes all the lines from the pattern buffer.

Hence it does not print anything on the standard output.

Point to the output

We can see the 4th line is deleted.

We can also give a range of line numbers that can be deleted.

This command deletes all the lines from 2 to 6.

This has deleted the lines which have the author name as R K Narayan.

> cat IndianBooks.txt

Highlight the text between Malgudi and Crescent.

>sed ‘/Malgudi/,/Crescent/d’ IndianBooks.txt

For example, we want to remove all the lines between the patterns Malgudi and Crescent.

Type sed space within single quotes forward slash Malgudi forward slash comma forward slash Crescent forward slash d space IndianBooks.txt

Look at the output.

Highlight $d

We can delete the last line of a file using the special character dollar $.

Highlight 1d

Type the command as shown.

Here ‘1’ specifies the line number of the file.

The negation operator with d indicates, not to delete the first line.

We can see this sed command removes all the lines except the first line.

We can specify the list of lines to be removed with semicolon as a delimiter.

Recall that the caret(^) symbol specifies the starting of a line.

We can see that line 1 and line 10 are deleted.

This command deletes all the lines that end with '3'.

$ dollar is to indicate the end of the line.

We can see that the lines ending with 3 in the published year are deleted.

Note that the lines ending with '3' or '8' in the published year are deleted.

It prints the content of the file on the Linux terminal by removing the lines.

To remove the lines from the source file itself, use hyphen i option with sed command.

Otherwise, you can redirect the output of the sed command to another file.

Write command

Then writes the pattern buffer to the given output file according to the given options.

Write command

Syntax: sed 'ADDRESS w outputfile' inputfile

Address can be either line numbers or pattern strings.

outputfile is the filename where the output has to be stored.

inputfile is the input file for the command to execute.

Note that sed creates an output file if it is not present and over writes if it is already present.

If you open books_copy.txt, you will see the copy of the content of IndianBooks.txt

> sed -n ‘1~2 w out.txt’ IndianBooks.txt

Type the command to copy all odd lines to another file.

We can see only the odd lines are copied to out.txt

We can give patterns that have to be copied to another file.

This command will store the books with author name Gandhi to another file.

Let us see the output file GandhiBooks.txt

Read Command

It appends with each line of the input file as specified in the sed command pattern.

Then it inserts after the 4th line in IndianBooks.txt

Here 4 specifies the line number and r specifies the read command.

Assignment

sed ‘4,6 r new_books.txt’ IndianBooks.txt

> sed ‘$ a 11. Broken wings, Sarojini Naidu, 1916’ IndianBooks.txt

Type the command with the new book entry as shown.

Here a indicates append command and $ dollar indicates the end of the file.

Type the command with line number as shown.

Here '6' indicates the line number and a is the append command.

Highlight /Hind Swaraj/

Look at the output.

The new book entry has appended after the pattern ‘Hind swaraj’.

Highlight /My/

If there are multiple patterns matching, then the text is appended after each match.

> sed ‘3 i 3. Our films, Their Films, Satyajit Ray, 1976’ IndianBooks.txt

Highlight 3 and ‘i’

But it inserts a line before a specific position.

Type the command as shown:

This command inserts the new text before the third line.

Here 3 is the line number and ‘i’ represents the insert command.

This command replaces the existing line with new text.

Type the command as shown.

‘c’ indicates the change command.

We can see the third line is replaced with the new text.

Type the command as shown.

The lines '6' to '8' are replaced with the new text.

>> sed ‘4 e date’ IndianBooks.txt

e represent the execute command.

This will execute the external command and insert at the matched pattern.

We can see the date is inserted at the fourth line.

Summary

• Delete command
• Write command
• Read command
• Append command
• Insert command
• Change command
• Execute command

Assignment:

> sed ‘4,6 r date’ IndianBooks.txt

> sed ‘/My/ e date’ IndianBooks.txt

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