Replacing Text in Files Using `sed` on Linux

If you work with multiple text files on Linux and need to replace specific text within them, the sed (Stream Editor) tool is a highly useful choice. In this guide, we’ll discuss how to use sed to efficiently replace text in text files.

What is sed?

sed is a command-line tool in Unix/Linux used for editing text in streams of data. It allows you to perform various editing operations such as searching, replacing, deleting, and inserting text.

Example Case: Replacing Text in Text Files

Suppose you have several text files in your directory and want to replace all occurrences of the string abc with aab. Here’s how to do it using sed.

Step 1: Understanding the sed Command

The basic command used for text replacement with sed is:

sed 's/pattern/replacement/g'

Here:

• s is the command for substitution.
• pattern is the text you want to replace.
• replacement is the text that will replace the pattern.
• g at the end of the command indicates that the replacement should be applied to all occurrences in the line (global).

Step 2: Using sed to Replace Text in Files

To replace text in all files with a .txt extension in your directory, use the following command:

sed -i 's/abc/aab/g' *.txt

Let’s break down this command:

• sed is the command to run the Stream Editor.
• -i is an option that tells sed to perform the replacement directly in the file, without making a copy.
• 's/abc/aab/g' is the replacement pattern that searches for the string abc and replaces it with aab.
• *.txt specifies that this operation should be applied to all files with a .txt extension in the current directory.

Practical Example

Suppose you have two text files:

• file1.txt containing:

  abc is a test
  another abc here

• file2.txt containing:

  abc in this file too

After running the command:

sed -i 's/abc/aab/g' *.txt

Your file contents will be updated to:

• file1.txt:

  aab is a test
  another aab here

• file2.txt:

  aab in this file too

Tips and Tricks

• Backup Before Editing: If you want to create a backup of the files before editing, you can use the -i.bak option. Example: sed -i.bak 's/abc/aab/g' *.txt will create a backup file with a .bak extension before modifying the original files.

• Replacement with Regular Expressions: sed also supports regular expressions, allowing for more complex search and replace operations.

• Check Results Before Changing: To preview the replacement results without modifying the files, you can run the command without the -i option. Example: sed 's/abc/aab/g' *.txt.

Conclusion

sed is a powerful tool for text editing in streams of data. By understanding how to use the replacement command, you can quickly and efficiently edit text across multiple files. Always ensure to check results and create backups if necessary before making permanent changes.