How to Replace the First Line in Linux Files

Sometimes, you need to change the first line in a file on your Linux system. This might be to update a configuration, correct a mistake, or add some new information. This guide will show you how to easily replace the first line in a file using simple commands.

Using the sed Command

The sed command is a powerful tool for editing files in Linux. You can use it to replace text, delete lines, and perform many other tasks. Here, we will use it to replace the first line of a file.

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Step-by-Step Instructions

1. Create a Sample File: First, let’s create a sample file to work with. Use the following command to create a file named sample.txt with some text.

   
   echo -e "First Line\nSecond Line\nThird Line" > sample.txt
   
   

   This command will create a file named sample.txt with three lines of text.

2. View the File: You can view the contents of the file using the cat command.

   
   cat sample.txt
   
   

   You should see the following output:

   
   First Line
   Second Line
   Third Line
   
   

3. Replace the First Line: Now, let’s replace the first line with new text. Use the following sed command:

   
   sed -i '1s/.*/New First Line/' sample.txt
   
   

   This command breaks down as follows:

   • -i: Edit the file in place.
   • '1s/.*/New First Line/': This part tells sed to substitute (s) the first line (1) with “New First Line”. The .* matches the entire line.
4. View the Updated File: Check the file again to see the changes.

   
   cat sample.txt
   
   

   You should see the following output:

   
   New First Line
   Second Line
   Third Line
   
   

Conclusion

Using the sed command, you can easily replace the first line in a file on your Linux system. This is a simple yet powerful way to update files without manually editing them. By following these steps, you can quickly make changes to your files and streamline your workflow.