Guide to using the “sed” command in Linux

sed is a stream editor in Linux that is used to perform basic text transformations on an input stream (a file or input from a pipeline). This guide will provide examples of how to use the sed command.

Syntax

The basic syntax of the sed command is as follows:

$ sed [options] 'command' file

• options: optional flags to modify the behavior of the sed command.
• command: the text transformation to be performed.
• file: the input file to be edited (or omitted for standard input).

Basic Usage

Replacing text

One of the most common uses of sed is to replace text in a file. To replace a string in a file, the following syntax is used:

$ sed 's/old-text/new-text/g' file

The s indicates that we are using the substitution command, old-text is the text to be replaced, new-text is the text to replace it with, and the g at the end indicates that all occurrences of old-text should be replaced (without g, only the first occurrence in each line would be replaced).

Printing specific lines

$ sed -n '3,5p' file

This will print lines 3 to 5 from the file. The -n option tells sed to only print the specified lines and not all lines in the file.

Advanced Usage

Using Regular Expressions

sed supports basic regular expressions, which can be used to match and replace text based on patterns. The following example shows how to use a regular expression to replace all occurrences of a number in a file:

$ sed 's/[0-9]/X/g' file

This will replace all occurrences of numbers in the file with the letter X.

Deleting Lines

You can use sed to delete specific lines from a file. The following syntax will delete lines 3 to 5:

$ sed '3,5d' file

Inserting Lines

You can also insert new lines into a file using sed. The following syntax will insert a new line after line 3:

$ sed '3a\This is a new line' file

Appending Text

You can append text to the end of a file using sed. The following syntax will append the text This is some text to the end of the file:

$ sed '$a\This is some text' file

Conclusion

In this guide, we covered the basic and advanced usage of the sed command in Linux. With these examples, you should be able to perform a variety of text transformations on your files.