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head and tail

The head and tail commands are essential Unix utilities for viewing parts of files. They allow you to quickly preview large files by displaying only the beginning or the end, respectively. Whether you need to inspect log files, sample data sets, or monitor real-time output, these commands are both simple and powerful. This comprehensive guide will walk you through the syntax, options, practical examples, and advanced techniques for using both head and tail.

Table of Contents

  1. Introduction

  2. The head Command


    2.1. Basic Syntax and How head Works


    2.2. Common Options and Parameters


    2.3. Practical Examples


    2.4. Advanced Usage Tips

  3. The tail Command


    3.1. Basic Syntax and How tail Works


    3.2. Common Options and Parameters


    3.3. Practical Examples


    3.4. Advanced Usage Tips

  4. Combining head and tail

  5. Conclusion and Further Reading

Introduction

When working with files that contain many lines, it is often impractical to load the entire file into a terminal or editor. The head and tail commands help by displaying only a portion of the file:

  • head: Shows the first part of a file.

  • tail: Shows the last part of a file.

Both tools are frequently used in shell scripting, log file analysis, and data processing tasks.

The head Command

Basic Syntax and How head Works

The basic syntax for head is:

head [OPTIONS] [FILE...]

By default, head prints the first 10 lines of each specified file. If no file is provided, it reads from standard input.

Common Options and Parameters for head

  • -n NUM or --lines=NUM:
    Display the first NUM lines.

    head -n 5 file.txt

  • -c NUM or --bytes=NUM:
    Display the first NUM bytes of the file.

    head -c 100 file.txt

  • Multiple Files:
    When given more than one file, head prints a header with the file name before its output.

    head file1.txt file2.txt

Practical Examples for head

  1. Display the first 10 lines (default):

    head logfile.txt

  2. Display the first 5 lines:

    head -n 5 data.csv

  3. Display the first 100 bytes:

    head -c 100 config.ini

  4. Preview multiple files:

    head -n 3 /etc/passwd /etc/group

Advanced Usage Tips for head

  • Piping and Redirection:
    You can use head in pipelines to limit output. For example, when combined with grep:

    grep "ERROR" server.log | head -n 20

    This prints only the first 20 matching lines.

  • Combining with Other Utilities:
    When paired with utilities like wc (word count), head can help summarize file content.

    head -n 50 data.txt | wc -l

    This confirms that there are 50 lines in the preview.

The tail Command

Basic Syntax and How tail Works

The basic syntax for tail is:

tail [OPTIONS] [FILE...]

By default, tail prints the last 10 lines of each specified file. If no file is provided, it reads from standard input.

Common Options and Parameters for tail

  • -n NUM or --lines=NUM:
    Display the last NUM lines.

    tail -n 15 logfile.txt

  • -c NUM or --bytes=NUM:
    Display the last NUM bytes.

    tail -c 50 logfile.txt

  • -f or --follow:
    Continuously monitor the file for new content (commonly used for logs).

    tail -f server.log

  • -F:
    Similar to -f but follows the file by name, which is useful if the file is rotated.

    tail -F server.log

Practical Examples for tail

  1. Display the last 10 lines (default):

    tail access.log

  2. Display the last 15 lines:

    tail -n 15 error.log

  3. Display the last 50 bytes:

    tail -c 50 report.txt

  4. Monitor a log file in real-time:

    tail -f /var/log/syslog

  5. Follow a file that might be rotated:

    tail -F /var/log/application.log

Advanced Usage Tips for tail

  • Combined with head:
    To extract a specific block of lines from the end of a file, you can combine tail with head. For example, to view lines 101–110 from the end:

    tail -n 110 file.txt | head -n 10

  • Using with Pipes:
    Just like head, tail works seamlessly in pipelines. For instance, to see the last few lines of a filtered output:

    grep "WARN" system.log | tail -n 5

  • Tracking File Changes:
    Use tail -f in conjunction with other monitoring tools (like multitail or custom scripts) to keep an eye on log file updates in real time.

Combining head and tail

Sometimes you might want to extract a specific range of lines from a file. By combining head and tail, you can achieve this easily. For example, to display lines 20 through 30 from a file:

head -n 30 file.txt | tail -n 11

This works as follows:

  • head -n 30 file.txt extracts the first 30 lines.

  • tail -n 11 then displays the last 11 lines of that output, which correspond to lines 20–30 of the original file.

Conclusion and Further Reading

The head and tail commands are powerful tools for quickly previewing and monitoring files. Whether you need a snapshot of the beginning of a file or you want to continuously watch the end of a log file, these utilities are indispensable for everyday command-line tasks. Their simplicity, combined with the ability to integrate them into more complex pipelines, makes them key components of any Unix/Linux user’s toolkit.

Further Reading and Resources

  • Manual Pages:
    Access detailed information by typing:

    man head man tail

  • Online Documentation:

  • Tutorials and Examples:
    Explore community forums, blogs, and Q&A sites like Stack Overflow for additional examples and creative uses of head and tail.

Experiment with these commands on your own data to see how they can help streamline your workflow. Happy previewing!

Last modified: 08 February 2025
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