Mastering Bash File Appending: Redirection vs. Tee Command

When working with Bash, appending text to a file is a common task, and fortunately, there are multiple methods to achieve this. This article explores various approaches to appending text to a file in Bash.

To append text to a file, ensure that you have the necessary write permissions; otherwise, you may encounter a permission denied error.

Append to a File using the Redirection Operator (>>)

The >> redirection operator allows you to append output to a specified file. Commonly used commands for printing text to the standard output and redirecting it to a file are echo and printf.

echo "this is a new line" >> file.txt

With the -e option, echo interprets backslash-escaped characters, such as newline (\n):

echo -e "this is a new line \nthis is another new line" >> file.txt

For more complex output, the printf command allows you to specify the formatting:

printf "Hello, I'm %s.\n" $USER >> file.txt

Another method is using the Here document (Heredoc) to pass multiple lines of input to a command:

cat << EOF >> file.txt
The current working directory is: $PWD
You are logged in as: $(whoami)
EOF

Appending the output of any command to a file is possible; for example, using the date command:

date +"Year: %Y, Month: %m, Day: %d" >> file.txt

When using redirection, be cautious not to overwrite important existing files with the > operator.

Append to a File using the tee Command

The tee command reads from standard input and writes to both standard output and one or more files simultaneously. To append output to a file, use tee with the -a or --append option:

echo "this is a new line" | tee -a file.txt

To prevent tee from writing to standard output, redirect it to /dev/null:

echo "this is a new line" | tee -a file.txt >/dev/null

tee has advantages over the >> operator, allowing simultaneous appending to multiple files and writing to files owned by other users with sudo.

To append text to a file without write permissions, use sudo with tee:

echo "this is a new line" | sudo tee -a file.txt

To append text to multiple files, specify the files as arguments:

echo "this is a new line" | tee -a file1.txt file2.txt file3.txt

Conclusion

Whether using the >> redirection operator or the tee command, appending text to a file in Bash offers flexibility based on your specific needs. The >> operator is simple and effective, while tee provides additional capabilities such as writing to multiple files and handling permissions with sudo. Choose the method that best suits your requirements.

Feel free to leave any questions or feedback in the comments.