head

Overview

The head command displays the first lines of files or input streams. By default, it shows the first 10 lines, making it useful for previewing file contents.

Syntax

head [options] [file...]

Common Options

Option Description
-n num Show first num lines
-c num Show first num bytes
-q Suppress headers
-v Always show headers
-z Line delimiter is NUL
--lines=num Same as -n
--bytes=num Same as -c

Key Use Cases

  1. Preview file contents
  2. Extract file headers
  3. Sample data examination
  4. Log file monitoring
  5. Quick file inspection

Examples with Explanations

Example 1: Default Usage

head file.txt

Shows first 10 lines of file

Example 2: Specific Line Count

head -n 5 file.txt

Shows first 5 lines

Example 3: Multiple Files

head -n 3 *.txt

Shows first 3 lines of each txt file

Example 4: Byte Count

head -c 100 file.txt

Shows first 100 bytes

Common Usage Patterns

  1. Quick file preview:

    head -20 logfile.log

  2. CSV header inspection:

    head -1 data.csv

  3. Combined with tail:

    head -50 file.txt | tail -10

Advanced Usage

  1. Suppress filename headers:

    head -q file1.txt file2.txt

  2. Always show headers:

    head -v file.txt

  3. Process substitution:

    head -5 <(command)

Performance Analysis

  • Very fast for small line counts
  • Efficient streaming operation
  • Minimal memory usage
  • Good for large files
  • Stops reading after required lines

Best Practices

  1. Use appropriate line counts
  2. Combine with other text tools
  3. Consider byte vs line counting
  4. Use for quick file validation
  5. Helpful for debugging scripts

Integration Examples

  1. Log analysis:

    head -100 /var/log/syslog | grep error

  2. Data sampling:

    head -1000 large_dataset.csv > sample.csv

  3. Script debugging:

    head -5 "$input_file" | while read line; do
    echo "Processing: $line"
done

Scripting Applications

  1. File validation:

    if head -1 "$file" | grep -q "^#"; then
    echo "File has header"
fi

  2. Quick content check:

    head -n 1 *.conf | grep -v "^#"