How to Append to File in Bash

Quick Answer: Append to File in Bash

To append content to a file in Bash, use the >> redirection operator: echo "text" >> file.txt. This adds content to the end of the file without overwriting existing content. Use > (single) to overwrite instead.

Quick Comparison: File Appending Methods

Method	Operator	Behavior	Best For
echo >>	>>	Append line	Simple text
cat >>	>>	Append block	Multiple lines
printf >>	>>	Formatted append	Precise formatting
tee -a	Pipe	Append + display	Logging
sed -i	In-place	Edit and append	Complex edits

Bottom line: Use >> for simple appending, use cat for multiple lines.

---

Append content to files in Bash.

Method 1: Using >> Operator

echo "New line" >> myfile.txt

Appends to end of file (creates if doesn’t exist).

Method 2: Append Multiple Lines

cat >> myfile.txt << EOF
Line 1
Line 2
Line 3
EOF

Method 3: Append Variable Content

text="Important data"
echo "$text" >> logfile.txt

Method 4: Append with Timestamp

echo "[$(date)] New entry" >> log.txt

Differences: > vs >>

Operator	Behavior
>	Overwrite file (create if missing)
>>	Append to file (create if missing)

Practical Examples

Append Log Entry

#!/bin/bash

log_file="/var/log/myapp.log"

log() {
  echo "[$(date +'%Y-%m-%d %H:%M:%S')] $*" >> "$log_file"
}

log "Application started"
log "Processing data"
log "Application ended"

Append with Condition

file="data.txt"

if [ -f "$file" ]; then
  echo "New data" >> "$file"
else
  echo "New data" > "$file"  # Create if missing
fi

Append Command Output

# Append system info
echo "--- System Info ---" >> syslog.txt
uname -a >> syslog.txt
df -h >> syslog.txt

Append Multiple Files

# Combine files
cat file1.txt file2.txt file3.txt > combined.txt

# Or append sequentially
cat file1.txt >> combined.txt
cat file2.txt >> combined.txt
cat file3.txt >> combined.txt

Safe Append Pattern

#!/bin/bash

file="$1"
content="$2"

if [ -z "$file" ] || [ -z "$content" ]; then
  echo "Usage: $0 <file> <content>"
  exit 1
fi

echo "$content" >> "$file"

if [ $? -eq 0 ]; then
  echo "Appended successfully"
else
  echo "ERROR: Failed to append"
  exit 1
fi

Key Points

• >> appends; > overwrites
• Always quote variables: echo "$var" >> "$file"
• Use dates/timestamps in logs for debugging
• Check for write permissions before appending

Common Use Cases

1. Logging - Append events and errors
2. Configuration - Add settings to config files
3. Data collection - Accumulate results
4. Backups - Combine multiple files