od Command in Linux
The od command in Linux dumps files in octal and other formats, such as hexadecimal, ASCII, and more. It is a handy command, especially for debugging binary files.
By default, the od command displays the contents of the specified file in octal. It treats multiple streams as a single file; if a dash (-) is specified, then it reads from standard input.
Table of Contents
Here is a comprehensive guide to the options available with the od command −
Syntax of od Command
The syntax of the od command is as follows −
od [options] [file]
The [options] field in the above syntax is used to specify options such as various output formats. The [file] is used to specify the file that needs to be displayed in the specified format.
od Command Options
The options of the od command are listed below −
| Flags | Options | Description |
|---|---|---|
| -A | --address-radix=RADIX | Choose the base for file offsets [doxn](d for decimal, o for octal, x for hexadecimal, n for none) |
| -j | --skip-bytes=BYTES | Skip the first BYTES of input |
| -N | --read-bytes=BYTES | Limit output to BYTES of input |
| -S | --strings[=BYTES] | Display strings of at least BYTES printable characters [default is 3] |
| -t | --format=TYPE | Select output format(s) (x for hexadecimal, c for ASCII) |
| -v | --output-duplicates | Show all lines, avoiding * for repeated lines |
| -w | --width[=BYTES] | Set line width to BYTES [default is 16] |
| --traditional | Enable traditional argument handling | |
| --help | Show usage help and exit | |
| --version | Display version info and exit |
The shorthand of various format types is listed below −
| Types | Equivalent to | Description |
|---|---|---|
| -a | -t a | Displays named characters (ignores the high-order bit) |
| -b | -t o1 | Displays octal bytes |
| -c | -t c | Displays printable characters or backslash escapes |
| -d | -t u2 | Displays unsigned decimal 2-byte units |
| -f | -t fF | Displays floating-point numbers |
| -i | -t dI | Displays signed decimal integers |
| -l | -t dL | Displays signed decimal long integers |
| -o | -t o2 | Displays octal 2-byte units |
| -s | -t d2 | Displays signed decimal 2-byte units |
| -x | -t x2 | Displays hexadecimal 2-byte units |
The above formats can be specified directly or by using the -t option.
Examples of od Command in Linux
In this section, the usage of od command will be discussed with examples. The context of the text file used in the following examples is shown below −
Displaying File Contents to Octal Bytes
By default, the od command displays the contents of the specified input in octal byte format. To display the contents of a text file in octal bytes, use the following command −
od file.txt
Displaying File Contents in Hexadecimal
To display the file contents in hexadecimal, use the -x option −
od -x file.txt
Displaying File Contents in Floating Point Numbers
To display the file contents in floating point numbers, use the -f option −
od -f file.txt
Displaying File Contents with Named Characters
Named characters are symbolic representations of characters used in text encoding systems, specifically those that are non-printable or control characters. To display the named characters of a file, use the -a option −
od -a file.txt
This mode helps in identifying non-printable characters by showing them with their symbolic names, which makes it easier to understand control sequences in the file. Common named characters are listed below −
- sp = space
- nl = newline \n
- tab = \t
- cr = carriage return \r
- bs = backspace
- esc = escape \e
Displaying Printable Characters with Escape Sequences
To show printable characters and escape sequences, use the -c option with the od command −
od -c file.txt
Skipping Bytes
To skip bytes, use the -j or --skip-bytes option with the number of bytes. For example, to skip the first 7 bytes, use the following command −
od -j 7 -c file.txt
Reading Specific Number of Bytes
To read a specific number of bytes, use the -N or --read-bytes option with the number of bytes. For example, to read the first 6 bytes, use the od command in the following way −
od -N 6 -c file.txt
The -N option limits the number of bytes read from the file.
Displaying a Specific Number of Bytes Per Line
To display a specific number of bytes per line, use the -w or --width option with the od command. To display 7 bytes per output line, use the od command in the following way −
od -w7 -c file.txt
Saving the Output to a File
To save the displayed output to a file, use the redirection operator (>) with the file name.
od file.txt > output.txt
Getting Input from the Command Line
To specify input in the command line, use the dash (-) after the od command and option −
od -x -
First type the command and press Enter −
Type the string to be converted and press Enter. Lastly, press the ctrl+d to display the output as shown below −
Changing File Offset Base
To change the file offset base, use the -A or --address-radix option with [doxn]. The d is for decimal, o for octal, x for hexadecimal, and n for none.
od -A d file.txt
Conclusion
The od command in Linux is a handy tool for displaying file contents in various formats, including octal, hexadecimal, and ASCII. It offers options to skip bytes, limit output, adjust line width, and convert data into different formats, making it essential for analyzing binary files and debugging.
In this tutorial, we explained the od command, its syntax, options and usage in Linux with examples.