head — Linux basic command

Linux / Basic Linux commands / head.html

A command that prints only the beginning part (the first few lines) of a file.

Basic Information

What is this command?

head is a command that outputs only the specified number of lines (default 10 lines) from the beginning of a file. It is used to quickly check the first part of a long file.

You can specify the number of output lines with the -n option, and also output based on the number of bytes with the -c option.

What problem does it solve?

• Checks the beginning of a long file.
• Quickly checks header information.
• Looks at the beginning part to understand the file structure.
• Previews only the front part of a large file.

Main Features

Default 10-Line Output

Prints the first 10 lines of a file.

• Use Case: When you need to quickly grasp the file structure.
• Result Obtained: You can view the content at the beginning of the file.
• Limitations: If the file has fewer than 10 lines, the entire content is printed.

Specify Number of Lines (-n)

Specify the number of lines to output with the -n option.

• Use Case: When you only want to check a specific number of lines.
• Result Obtained: Outputs exactly the specified number of lines.
• Limitations: An error occurs if a value of 0 or less is specified.

Output by Byte Count (-c)

Outputs based on the number of bytes using the -c option.

• Use Case: When reading fixed-length record files.
• Result Obtained: Outputs the specified number of bytes.
• Limitations: Multi-byte characters like Hangul may be truncated.

Simultaneous Output of Multiple Files

Outputs the beginning parts of multiple files in sequence.

• Use Case: When checking the beginning of multiple log files at once.
• Result Obtained: Outputs each file with its header.
• Limitations: Output can become lengthy if there are many files.

Installation and Execution

Verify Default Installation

It is included by default in all Linux distributions.

which head
head --version

Installation (Lightweight Environment)

Typically already installed.

sudo apt install coreutils   # Debian/Ubuntu

Practical Usage Examples

Default Output

Check the first 10 lines of a file.

# Print the first 10 lines
cat /var/log/syslog | head

# Specify file directly
head /var/log/syslog

# Multiple files
head file1.txt file2.txt

Specify Number of Lines

Outputs the desired number of lines.

# Only the first 5 lines
head -n 5 /var/log/syslog

# Only the first 20 lines
head -20 /var/log/syslog

# With a pipe
ps aux | head -5

Output by Byte Count

Outputs based on the number of bytes.

# Print only the first 100 bytes
head -c 100 /var/log/syslog

# Only the first line (head -1)
head -1 /etc/passwd