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od: Output Octal/Hexadecimal Dump of Files

The `od` command outputs the contents of a file in various formats such as octal and hexadecimal. It is a traditional tool used to analyze the contents of binary files or to check for invisible special characters in text files. It provides similar functionality to `hexdump`.

Overview

od (octal dump) is a utility that reads file contents byte by byte and converts them into various human-readable formats. As its name 'octal' suggests, it primarily outputs in octal format, but through options, it can also output in hexadecimal, decimal, etc. While `hexdump` is mainly used for hexadecimal output, `od` is characterized by offering more output formats and control options. It is also utilized for binary file structure analysis and data forensics.

Key Features

The key features of the `od` command are as follows:

  • Converts and outputs file contents in octal, hexadecimal, decimal, etc.
  • Suitable for binary file analysis and debugging.
  • Provides powerful options to specify various formats and output layouts.
  • Can process the output of other commands via pipes (|).

Differences from hexdump

od and hexdump are functionally similar, but they differ in detailed output methods and options.

  • od: Default output is octal, and it supports dumping a wider range of data types (integers, floating-point numbers, etc.).
  • hexdump: Default output is hexadecimal, and its primary format is `canonical`, which shows offset, hexadecimal values, and ASCII strings together.

Key Options

Commonly used `od` command options are grouped by purpose.

1) Output Format Control

2) Filtering and Control

3) Help

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Usage Examples

Learn the functionalities of the `od` command through various usage examples.

Output File Contents in Octal

od /bin/cat | head

Outputs the contents of the binary file `/bin/cat` in octal. This is the default behavior of `od`.

Output in Hexadecimal and ASCII Characters

echo 'Hello World!' | od -t x1c

Outputs file contents simultaneously in hexadecimal bytes and ASCII characters. The `-t x1c` option is a format that outputs hexadecimal (x1) and ASCII characters (c) together.

Output Only a Specific Part of a File

od -t x1 -N 100 /bin/ls

Outputs 100 bytes of content from the beginning of the `/bin/ls` file in hexadecimal.

Analyze File with Newline Characters

echo 'Hello\nWorld' | od -c

Checks the contents of a text file containing newline (`\n`) characters in ASCII characters and octal codes. `012` is the octal code for a newline.

Tips & Cautions

Important points to note when using the `od` command are summarized here.

Tips

  • `od` provides more diverse output formats (via the `-t` option) than `hexdump`, making it useful for interpreting dumped data in various data types.
  • When running the `od` command, outputting the entire file can freeze the terminal. Therefore, it's recommended to limit the output length using the `-N` option or by piping to the `head` command.
  • The output format of `od` is not identical to `hexdump`'s `-C` option, so for a more familiar layout, `hexdump` might be more convenient to use.

Related commands

These are commands that are functionally similar or are commonly used together.

hexdump

hexdump: Output Hexadecimal Dump of a File

strings

strings: Extracting Strings from Binary Files

xxd

xxd: Hex Dump and Reverse Conversion Tool

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cat Command Guide: View and Concatenate File Contents

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