Linux seq Command with Practical Examples

Introduction

In this lab, you will learn how to use the Linux seq command, which is a versatile tool for generating numeric sequences. The lab covers the purpose and syntax of the seq command, and provides practical examples on how to customize the output, such as adjusting the step size, formatting, and padding. This knowledge can be useful in various scripting and automation tasks.

The lab starts by explaining the basic syntax of the seq command and demonstrating how to generate simple numeric sequences. It then explores more advanced features, allowing you to create sequences with specific starting and ending points, as well as control the step size and formatting of the output. By the end of the lab, you will have a solid understanding of how to effectively use the seq command to meet your needs.

Linux Commands Cheat Sheet

Skills Graph

Understand the Purpose and Syntax of the seq Command

In this step, you will learn about the purpose and syntax of the seq command in Linux. The seq command is a versatile tool that generates numeric sequences, which can be useful in various scripting and automation tasks.

The basic syntax of the seq command is:

seq [options] [start] [step] stop

Here's what each part of the syntax means:

• start: The starting number of the sequence (default is 1).
• step: The increment or decrement between each number in the sequence (default is 1).
• stop: The ending number of the sequence.
• options: Various options to customize the output, such as formatting, padding, and more.

Let's try some examples to understand the seq command better.

First, let's generate a simple sequence of numbers from 1 to 5:

seq 5

Example output:

1
2
3
4
5

Now, let's generate a sequence with a different starting point and step size:

seq 2 2 10

Example output:

2
4
6
8
10

In this example, the sequence starts from 2, increments by 2, and ends at 10.

You can also use negative values to generate a descending sequence:

seq 10 -2 0

Example output:

10
8
6
4
2
0

The seq command provides several options to customize the output, such as:

• -f or --format: Specify a printf-style format string to format the output.
• -w or --equal-width: Pad the output with leading zeros to make all numbers have the same width.
• -s or --separator: Specify a custom separator between the numbers (default is a newline).

We'll explore more of these options in the next steps.

Generate Numeric Sequences with the seq Command

In this step, you will learn how to use the seq command to generate various numeric sequences.

Let's start by generating a sequence of numbers from 1 to 10:

seq 10

Example output:

1
2
3
4
5
6
7
8
9
10

You can also specify a starting number and an ending number:

seq 5 10

Example output:

5
6
7
8
9
10

To generate a sequence with a specific step size, use the start step stop format:

seq 1 2 10

Example output:

1
3
5
7
9

In this example, the sequence starts from 1, increments by 2, and ends at 10.

You can also use negative values to generate a descending sequence:

seq 10 -2 0

Example output:

10
8
6
4
2
0

The seq command can be useful in various scenarios, such as:

• Generating a range of numbers for use in shell scripts or automation tasks.
• Creating test data or sample input for programs.
• Iterating over a range of values in a loop.

Let's explore some more advanced options in the next step.

Customize Numeric Sequences with Step Size and Formatting

In this step, you will learn how to customize the output of the seq command by using various options to control the step size and formatting.

Let's start by generating a sequence with a custom step size:

seq 1 3 10

Example output:

1
4
7
10

In this example, the sequence starts from 1, increments by 3, and ends at 10.

You can also use the -f or --format option to specify a custom output format using a printf-style format string:

seq -f "Value: %.2f" 1 0.5 3

Example output:

Value: 1.00
Value: 1.50
Value: 2.00
Value: 2.50
Value: 3.00

In this example, the %.2f format specifier is used to display the numbers with two decimal places.

Another useful option is -w or --equal-width, which pads the output with leading zeros to make all numbers have the same width:

seq -w 01 02 10

Example output:

01
02
03
04
05
06
07
08
09
10

You can also use the -s or --separator option to specify a custom separator between the numbers (the default is a newline):

seq -s ", " 1 5

Example output:

1, 2, 3, 4, 5

These options can be combined to create more complex and customized numeric sequences. Experiment with different combinations to see how the seq command can be tailored to your needs.

Summary

In this lab, you first learned about the purpose and syntax of the seq command in Linux, which is used to generate numeric sequences. The basic syntax includes the starting number, step size, and ending number. You explored examples of generating simple sequences, sequences with different starting points and step sizes, as well as descending sequences. Additionally, you learned about various options to customize the output, such as formatting, padding, and specifying a custom separator. In the second part of the lab, you delved deeper into generating numeric sequences using the seq command, covering more advanced use cases and exploring the versatility of this tool.

Linux Commands Cheat Sheet