head

The head command in Unix and Linux is used to display the beginning of a file or piped data. By default, it shows the first 10 lines of each file it processes, but you can customize the number of lines or bytes displayed.

Basic Usage

The basic syntax for the head command is:

head [options] [file...]

• options: Command-line options to control the behavior of head.

• file: The file(s) to be processed. If no file is specified, head reads from standard input.

Examples

Displaying the First 10 Lines of a File

To display the first 10 lines of a file:

head file.txt

Displaying a Custom Number of Lines

To display the first n lines of a file, use the -n option followed by the number of lines:

head -n 5 file.txt

This command displays the first 5 lines of file.txt.

Displaying a Custom Number of Bytes

To display the first n bytes of a file, use the -c option followed by the number of bytes:

head -c 20 file.txt

This command displays the first 20 bytes of file.txt.

Displaying Multiple Files

To display the first 10 lines of multiple files:

head file1.txt file2.txt

Output:

==> file1.txt <==
first 10 lines of file1.txt

==> file2.txt <==
first 10 lines of file2.txt

Piping Output to head

You can pipe the output of other commands into head to view the first few lines of the output:

ls -l | head

This command displays the first 10 lines of the ls -l output.

Options

-n Option: Number of Lines

To specify the number of lines to display:

head -n 15 file.txt

This command displays the first 15 lines of file.txt.

-c Option: Number of Bytes

To specify the number of bytes to display:

head -c 50 file.txt

This command displays the first 50 bytes of file.txt.

-v Option: Always Print Headers

To always print headers when multiple files are provided, use the -v option:

head -v file1.txt file2.txt

This command ensures that headers are printed even if only one file is processed.

-q Option: Never Print Headers

To suppress headers when multiple files are provided, use the -q option:

head -q file1.txt file2.txt

This command prevents headers from being printed for each file.

Practical Use Cases

Previewing Files

When you want to quickly preview the beginning of a file, head provides a convenient way to do so without opening the entire file in an editor.

Monitoring Log Files

When analyzing log files, you can use head to view the most recent entries (especially in combination with tail).

Debugging Scripts

When debugging scripts that produce a large amount of output, you can pipe the output to head to see only the initial part of the output for quick analysis.

Summary

The head command is a simple yet powerful utility for viewing the beginning of files or piped data in Unix and Linux environments. Its flexibility in displaying a custom number of lines or bytes, combined with its ability to handle multiple files, makes it an essential tool for file and data inspection.

help

Usage: head \[OPTION]... \[FILE]... Print the first 10 lines of each FILE to standard output. With more than one FILE, precede each with a header giving the file name.

With no FILE, or when FILE is -, read standard input.

Mandatory arguments to long options are mandatory for short options too. -c, --bytes=\[-]NUM print the first NUM bytes of each file; with the leading '-', print all but the last NUM bytes of each file -n, --lines=\[-]NUM print the first NUM lines instead of the first 10; with the leading '-', print all but the last NUM lines of each file -q, --quiet, --silent never print headers giving file names -v, --verbose always print headers giving file names -z, --zero-terminated line delimiter is NUL, not newline --help display this help and exit --version output version information and exit

NUM may have a multiplier suffix: b 512, kB 1000, K 1024, MB 1000_1000, M 1024_1024, GB 1000_1000_1000, G 1024_1024_1024, and so on for T, P, E, Z, Y. Binary prefixes can be used, too: KiB=K, MiB=M, and so on.

man

NAME head - output the first part of files

SYNOPSIS head [OPTION]... [FILE]...

DESCRIPTION Print the first 10 lines of each FILE to standard output. With more than one FILE, pre‐ cede each with a header giving the file name.

   With no FILE, or when FILE is -, read standard input.

   Mandatory arguments to long options are mandatory for short options too.

   -c, --bytes=[-]NUM
          print the first NUM bytes of each file; with the leading '-',  print  all  but  the
          last NUM bytes of each file

   -n, --lines=[-]NUM
          print  the first NUM lines instead of the first 10; with the leading '-', print all
          but the last NUM lines of each file

   -q, --quiet, --silent
          never print headers giving file names

   -v, --verbose
          always print headers giving file names

   -z, --zero-terminated
          line delimiter is NUL, not newline

   --help display this help and exit

   --version
          output version information and exit

   NUM may have a multiplier suffix: b 512, kB 1000, K 1024, MB 1000*1000,  M  1024*1024,  GB
   1000*1000*1000,  G  1024*1024*1024,  and  so on for T, P, E, Z, Y.  Binary prefixes can be
   used, too: KiB=K, MiB=M, and so on.