sed linux

How to use SED command to delete lines in Linux

   What is SED ? –> Birth of SED

     Sed command can be used to delete or remove specific lines which matches a given pattern or in a particular position in a file. Here we will see how to delete lines using sed command with various examples.

The following file contains a sample data which is used as input file in all the examples:

Sed Command to Delete Lines – Based on Position in File

In the following examples, the sed command removes the lines in file that are in a particular position in a file.

1. Delete first line or header line

The d option in sed command is used to delete a line. The syntax for deleting a line is:

Here N indicates Nth line in a file. In the following example, the sed command removes the first line in a file.

2. Delete last line or footer line or trailer line

The following sed command is used to remove the footer line in a file. The $ indicates the last line of a file.

3. Delete particular line

This is similar to the first example. The below sed command removes the second line in a file.

4. Delete range of lines

The sed command can be used to delete a range of lines. The syntax is shown below:

Here m and n are min and max line numbers. The sed command removes the lines from m to n in the file. The following sed command deletes the lines ranging from 2 to 4:

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5. Delete lines other than the first line or header line

Use the negation (!) operator with d option in sed command. The following sed command removes all the lines except the header line.

6. Delete lines other than last line or footer line

7. Delete lines other than the specified range

Here the sed command removes lines other than 2nd, 3rd and 4th.

8. Delete first and last line

You can specify the list of lines you want to remove in sed command with semicolon as a delimiter.

9. Delete empty lines or blank lines

The ^$ indicates sed command to delete empty lines. However, this sed do not remove the lines that contain spaces.

Sed Command to Delete Lines – Based on Pattern Match

In the following examples, the sed command deletes the lines in file which match the given pattern.

10. Delete lines that begin with specified character

^ is to specify the starting of the line. Above sed command removes all the lines that start with character ‘u’.

11. Delete lines that end with specified character

$ is to indicate the end of the line. The above command deletes all the lines that end with character ‘x’.

12. Delete lines which are in upper case or capital letters

13. Delete lines that contain a pattern

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14. Delete lines starting from a pattern till the last line

Here the sed command removes the line that matches the pattern fedora and also deletes all the lines to the end of the file which appear next to this matching line.

15. Delete last line only if it contains the pattern

Here $ indicates the last line. If you want to delete Nth line only if it contains a pattern, then in place of $ place the line number.

Note: In all the above examples, the sed command prints the contents of the file on the unix or linux terminal by removing the lines. However the sed command does not remove the lines from the source file. To Remove the lines from the source file itself, use the -i option with sed command.

If you dont wish to delete the lines from the original source file you can redirect the output of the sed command to another file.

   

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