How to append to file with Bash - Append

Introduction

When working with Bash, there may be times when you need to add text to a file. Fortunately, there are several ways to accomplish this task. This article explains some of them.

To add text to a file, you must have write permissions on it. Otherwise, you will receive a permission denied error.

Append to a file using the redirection operator (>>)

Redirection allows you to take the output from one command and send it as input to another command or file. The >> redirection operator appends the output to a given file.

There are a number of commands you can use to print text to standard output and redirect it to the file. The two most commonly used commands for this purpose are echo and printf.

To add text to a file, run the command that prints the text and specifies the file name after the redirection operator:

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

When used with the -e option, the echo command interprets backslash characters as newlines \n:

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

To produce more complex output, you can use the printf command, which allows you to specify the formatting of the output:

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

Another way to add text to a file is to use the Here document (Heredoc). It's a type of redirection that allows you to pass multiple lines of input to a command.

For example, you can pass the contents to the cat command and add it to a file:

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

You can add the output of any command to a file. Here is an example with the date command:

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

When appending to a file using a redirect, be careful not to use the > operator to overwrite an existing important file.

Add to a file using the tee command

tee is a Linux command line utility that reads from standard input and writes to both standard output and one or more files simultaneously.

By default, the tee command overwrites the specified file. To append the output to the file use tee with the -a ( --append ) option:

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

If you don't want tee write to standard output, redirect it to /dev/null:

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

The advantage of using the tee command over >> operator is that tee allows you to simultaneously add text to multiple files and write to files owned by other users in conjunction with sudo.

To add text to a file for which you do not have write permissions, prepend it with sudo like tee shown below:

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

tee receives the output of the echo command, elevates sudo permissions, and writes to the file.

To add text to more than one file, specify the files as arguments to the tee command:

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

Conclusion

If you're working with Linux and need to add text to an existing file, you have a couple of options. One way is to use the redirect >> operator, which will append the text to the end of the file without overwriting any existing content. Another option is to use the tee command, which not only adds the text to the file, but also displays it on the screen as it is added.

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