Using the 'head' Command in Linux (with examples)

The head command in Linux is a powerful utility used to output the first part of files. This command can provide multiple ways to selectively display the beginning portions of a file, making it an essential tool for anyone dealing with large files or logs. By using head, you can quickly preview data or inspect the start of a file without opening its entirety. An understanding of head and its options will enable you to streamline data handling and gain quick insights into your files.

Use case 1: Output the first few lines of a file

Code:

head --lines 10 path/to/file

Motivation:
When working with files containing a large amount of data, such as log files or datasets, it can be crucial to inspect the beginning of the file to understand its content, format, or structure. The first few lines often contain important information like headers or metadata. Using the head --lines count path/to/file is a quick way to access this information without having to open and scroll through the file manually.

Explanation:

• head: This is the command that signals the start of the operation to output the top section of the file.
• --lines 10: This option specifies that the first 10 lines of the file should be displayed. You can customize the number ‘10’ to suit how many lines you want to see.
• path/to/file: This is the placeholder for the actual path and name of the file you want to examine.

Example Output:

Line 1: This is the first line of the file.
Line 2: This is the second line of the file.
...
Line 10: This is the tenth line of the file.

Use case 2: Output the first few bytes of a file

Code:

head --bytes 1024 path/to/file

Motivation:
In some scenarios, the interest in file examination might revolve around the specific size of data rather than lines, such as when dealing with binary files or needing to check encoded data. Utilizing head --bytes allows you to extract and view a specified number of bytes, which can be incredibly useful for verifying file formats or confirming specific data arrangements within a set byte size.

Explanation:

• head: Command informing that the output pertains to the file’s beginning.
• --bytes 1024: This option dictates that the first 1024 bytes should be displayed. You can adjust ‘1024’ to match the byte count you need to check.
• path/to/file: Indicates the file path and name for the operation.

Example Output (First 1024 bytes as plain text or binary format, depending on the file type):

This is the content of the file that covers the first 1024 bytes...

Use case 3: Output everything but the last few lines of a file

Code:

head --lines -3 path/to/file

Motivation:
It is sometimes necessary to read through a file while skipping over specific trailing data entries, such as summary information or some kind of footer typically residing at the end of many structured documents. Using head --lines -count gives you control to overlook the final few lines and focus on the main body of the content.

Explanation:

• head: Signals that the command’s aim is to output from the top of the file.
• --lines -3: This tells the command to exclude the last 3 lines from the output. The negative sign before ‘3’ signifies subtraction from the total lines.
• path/to/file: Designates the path to the file from which the content, excluding last 3 lines, is drawn.

Example Output:

Line 1: Data
Line 2: More data
...
Line N-3: Penultimate data line

Use case 4: Output everything but the last few bytes of a file

Code:

head --bytes -2048 path/to/file

Motivation:
In cases where files end with binary or padding data unnecessarily inflating file size, or if you need to evaluate the primary content without clutter, head --bytes -count can be a crucial tool. This format is ideal for eliminating extraneous byte data and focusing on the core content up to that point.

Explanation:

• head: This command initializes output in terms of file’s beginning parts.
• --bytes -2048: Directs the command to ignore the last 2048 bytes. The use of the negative sign before ‘2048’ is crucial to emphasize exclusion of those bytes.
• path/to/file: Identifies the specific file to process, minus the ending 2048 bytes.

Example Output (Everything except last 2048 bytes as text or binary):

This file contains the primary data, excluding the trailing bytes...

Conclusion:

Using the head command is a practical solution when you need quick access to portions of a file without loading the entire content. Whether you’re focusing on lines or bytes, head offers versatility to inspect and manage files efficiently. These examples demonstrate simple yet powerful approaches, empowering users to harness the utility effectively for varied tasks, from troubleshooting to data exploration.