When working with Linux command line, the echo command combined with redirection operators is a fundamental way to manipulate file contents. The basic syntax you're probably familiar with is:

echo "text" > file.txt

This writes "text" to file.txt, overwriting any existing content. But what if you want to add content without erasing the existing data?

Linux provides the double greater-than symbol (>>) for appending content to files. This operator preserves existing content while adding new text at the end of the file.

echo "new content" >> existing_file.txt

Let's look at some common scenarios where appending is useful:

# Appending to log files
echo "$(date): Application started" >> /var/log/myapp.log

# Building configuration files
echo "server_name example.com;" >> /etc/nginx/conf.d/site.conf
echo "listen 80;" >> /etc/nginx/conf.d/site.conf

# Creating multi-line files
echo "Line 1" >> output.txt
echo "Line 2" >> output.txt
echo "Line 3" >> output.txt

For more complex scenarios, you can combine echo with other commands:

# Append command output
ls -l >> directory_listing.txt

# Append multiple lines with a single echo
echo -e "First line\nSecond line" >> multiline.txt

# Append with variable substitution
username=$USER
echo "User $username logged in at $(date)" >> access.log

When writing scripts, it's good practice to handle potential errors:

# Check if file exists and is writable
if [ -w logfile.txt ]; then
    echo "New entry" >> logfile.txt
else
    echo "Error: Cannot write to logfile.txt" >&2
fi

While echo is common, other tools can append content too:

# Using printf
printf "%s\n" "New content" >> file.txt

# Using cat with heredoc
cat <> file.txt
Additional content
More lines
EOF

Every Linux user knows the basic redirection operator > for sending command output to a file:

echo "Hello World" > log.txt

But this overwrites existing content. What if we need to preserve previous data?

Linux provides the >> operator for appending content:

echo "New log entry" >> log.txt

Let's see some real-world scenarios:

1. Continuous logging:

date >> server.log
echo "Server started successfully" >> server.log

2. Multi-line appends:

cat <> config.cfg
[New Section]
host = example.com
port = 8080
EOT

For production environments, consider these professional practices:

# Append with timestamp
echo "$(date +'%Y-%m-%d %T') - User logged in" >> auth.log

# Error-resistant append
{ echo "Important message"; some_command; } >> compound.log 2>&1

• Permission issues (use sudo if needed)
• File locking during concurrent writes
• Accidental use of > instead of >>

Other ways to append in Linux:

# Using printf
printf "Appended text\n" >> file.txt

# Using tee
echo "Via tee" | tee -a file.txt