Redirections: The Secret to Reading and Writing Text Files in Bash

Have you ever wanted to read or write to a text file from the command line in Bash? It’s actually quite simple, once you know the secret of redirections.

Requirements and Dependencies

Before we get started, make sure you have a Bash terminal and a text editor installed on your system. We will be using nano as the text editor in our examples, but you can use any text editor you prefer, like Vim.

The Power of Redirections

Bash allows you to redirect the output of a command to a file, or to read the input of a command from a file. This is done using the > and < symbols, respectively.

For example, if we want to save the output of the ls command to a file called itvraag.nl, we can use the following command:

ls > itvraag.nl

This will create a new file called itvraag.nl and fill it with the list of files and directories in the current directory.

To append the output of a command to an existing file, we can use the >> symbol instead of >. For example:

echo "Hello, world!" >> itvraag.nl

This will add the string “Hello, world!” to the end of the itvraag.nl file.

To read the input of a command from a file, we can use the < symbol. For example, if we want to sort the contents of the itvraag.nl file, we can use the following command:

sort < itvraag.nl

This will take the contents of the itvraag.nl file and sort them alphabetically.

Surprising Fact

Did you know that you can also use redirections to create pipes? A pipe is a way to chain multiple commands together, so that the output of one command becomes the input of the next. This is done using the | symbol.

For example, if we want to sort the contents of the itvraag.nl file and then save the sorted output to a new file called sorted.txt, we can use the following command:

sort < itvraag.nl > sorted.txt

This will take the contents of the itvraag.nl file, sort them alphabetically, and save the sorted output to a new file called sorted.txt.

Key Take-Aways

• Redirections allow you to read and write to text files from the command line in Bash.
• The > symbol is used to save the output of a command to a file, and the >> symbol is used to append the output to an existing file.
• The < symbol is used to read the input of a command from a file.
• You can use the | symbol to create pipes, which allow you to chain multiple commands together.

5 Examples or Tips to Increase Productivity

1. Use redirections to quickly save the output of a command to a file, rather than manually copying and pasting the output.
2. Use the >> symbol to append output to a file, rather than overwriting the contents of the file with the > symbol.
3. Use pipes to streamline complex tasks that require multiple steps. For example, you can use pipes to sort and filter data, or to perform multiple transformations on a file.
4. Use the tee command to redirect the output of a command to both the terminal and a file. This is useful for debugging or for creating log files.
5. Use the cat command to concatenate multiple files into one. This can be done by using the cat command followed by the names of the files to be concatenated, separated by spaces. For example: cat file1.txt file2.txt > combined.txt.

Additional Resources

For more information on redirections and pipes, you can refer to the Bash man-pages by typing man bash in the terminal. You can also use the help command to get a list of available Bash commands and their usage.

Challenge

Try using redirections and pipes to perform the following task:

• Create a file called numbers.txt containing the numbers 1 to 10, each on a separate line.
• Use pipes to sort the numbers in descending order and save the sorted output to a new file called sorted.txt.