How to Use the Command 'seq' (with examples)

The seq command is a versatile tool in Unix-like operating systems for generating sequences of numbers. Whether you need a simple list, customized numerical increments, or formatted output, seq provides powerful options to streamline numerical list creation directly in the command line. Understanding different options and behaviors of seq, you can generate and manipulate simple numeric sequences with ease.

Use case 1: Sequence from 1 to 10

Code:

seq 10

Motivation:

Generating a straightforward sequence from one to ten can be very useful in scripting where a set range of numbers is needed. This simple usage of seq allows users to quickly generate such a list without manually typing each number. It is particularly valuable in programming loops, data iteration, or for quickly testing numerical data inputs.

Explanation:

• 10: This is the sole argument provided to seq, indicating the end of the sequence. By default, seq presumes the start of the sequence to be 1, so seq 10 generates numbers from 1 to 10.

Example Output:

1
2
3
4
5
6
7
8
9
10

Use case 2: Every 3rd number from 5 to 20

Code:

seq 5 3 20

Motivation:

When working on tasks that require specific increments, such as stepping through a set of data points or configuring repeated intervals, generating every third number in a sequence simplifies the process. This use case allows for a concise and computationally efficient way to generate interval-based sequences without manually calculating each step.

Explanation:

• 5: This is the start number for the sequence.
• 3: This is the increment value by which each subsequent number in the sequence increases.
• 20: This is the end number which should not be exceeded.

Example Output:

5
8
11
14
17
20

Use case 3: Separate the output with a space instead of a newline

Code:

seq -s " " 5 3 20

Motivation:

Formatting output is key in command-line operations, especially when preparing data for immediate human readability or for piping into another command. Separating output numbers with spaces rather than the default newlines can be advantageous when inputs need to be condensed into a single line, suitable for configuration or flat file imports.

Explanation:

• -s " ": This option replaces the default newline separator with a specified string (in this case, a single space).
• 5, 3, 20: Maintains the same role as in the prior example, specifying the sequence’s start, increment, and end.

Example Output:

5 8 11 14 17 20

Use case 4: Format output width to a minimum of 4 digits padding with zeros as necessary

Code:

seq -f "%04g" 5 3 20

Motivation:

This use case is invaluable when sequences need formatting to a particular width, such as when dealing with datasets requiring uniform column widths, or when preparing number sequences for file names, maintaining lexical sorting order when numbers are treated as strings.

Explanation:

• -f "%04g": This option denotes the format to be applied to each number. The format string "%04g" specifies a minimum width of 4 digits for each number, adding leading zeros as padding where necessary.
• 5, 3, 20: Similarly defines the sequence as in previous examples, providing start, increment, and end numbers.

Example Output:

0005
0008
0011
0014
0017
0020

Conclusion:

The seq command is an essential tool for anyone working with numerical sequences in the command line. By understanding its range of options—from simple sequences to specialized formatted outputs—you can leverage seq for a multitude of scripting and command-line tasks. Each use case demonstrates seq’s ability to enhance efficiency and accuracy in generating sequences tailored to specific requirements.