indent Command in Linux

Introduction to Code Formatting with the Linux indent Command

This tutorial guides you through using the Linux indent command for formatting C/C++ source code. The indent command is a valuable systemadmin tool that ensures consistent code formatting by automatically indenting code according to predefined or custom rules. This improves readability and maintainability. You'll begin by understanding the purpose and basic syntax of the indent command. Next, you'll learn how to apply it to format your C/C++ code. Finally, you'll delve into customizing indent command options to tailor the formatting to your preferred coding style.

Understanding the Purpose and Syntax of the indent Command

This section focuses on the purpose and syntax of the indent command within the Linux environment. The indent command serves as a formatter for C/C++ source code, ensuring consistent indentation based on a set of rules.

Let's start with the fundamental syntax of the indent command:

indent [options] input-file [output-file]

Here's what each part of the command signifies:

  • indent: The name of the command itself.
  • [options]: These are the various options you can use to customize the formatting of the code.
  • input-file: The C/C++ source code file you wish to format.
  • [output-file]: An optional parameter specifying where the formatted code should be saved. If omitted, the original input file will be overwritten with the formatted version. Exercise caution when omitting the output file to prevent accidental data loss.

Frequently used options for the indent command include:

  • -bad: Causes function calls and declarations to be broken across multiple lines.
  • -bap: Breaks function parameters across multiple lines.
  • -bbo: Places braces on "begin" lines.
  • -nbc: Prevents function calls from being broken across multiple lines.
  • -br: Also places braces on "begin" lines.
  • -brs: Places braces on "begin" lines, but with a space before the brace.
  • -ce: Positions comments to the right of code.
  • -cli: Indents comments to a specified column.

Example output:

$ indent --help
Usage: indent [options] input-file [output-file]
Options:
  -bad       Break after boolean and arithmetic operators
  -bap       Break after parameters in function declarations
  -bbo       Put braces on "begin" lines
  -nbc       Don't break function calls across lines
  -br        Put braces on "begin" lines
  -brs       Put braces on "begin" lines with a space
  -ce        Put comments to the right of code
  -cli       Indent comments to column N
  ...

In the following section, you will learn how to apply the indent command to automatically format your C/C++ source code.

Formatting C/C++ Source Code with the indent Command

This section will guide you through using the indent command to automatically format C/C++ source code, improving its readability and consistency.

Let's start by creating a basic C file as an example:

$ cd ~/project
$ nano sample.c

Paste the following code into the sample.c file:

#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

Now, run the indent command to format the source code:

$ indent sample.c

This command will create a new file named sample.c.indent containing the formatted code. Alternatively, you can explicitly specify the output file:

$ indent sample.c -o formatted_sample.c

This will generate a new file named formatted_sample.c containing the formatted code.

Example output:

$ cat formatted_sample.c
#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

As you can observe, the indent command has automatically indented the code according to its default formatting rules.

You can customize the formatting by using command-line options. For instance, to apply the "Linux" code formatting style, execute:

$ indent -linux sample.c -o formatted_sample.c

This command applies the "Linux" coding style to the formatted code.

The next step demonstrates how to further customize the indent command options to match your specific coding preferences.

Customizing indent Command Options for Specific Coding Styles

This section explains how to tailor the indent command options to format C/C++ source code according to particular coding style guidelines.

The indent command provides a comprehensive set of options for customization. Let's examine some frequently used options and their functionalities:

  1. Brace Placement:

    • -br (default): Places opening braces on the same line as the statement that begins the block.
    • -brs: Similar to -br, but adds a space before the opening brace.
    • -bl: Places opening braces on a new line after the statement that begins the block.

  2. Indentation:

    • -i<number>: Sets the indentation level to <number> spaces. This specifies how many spaces each level of indentation should have.
    • -ci<number>: Sets the continuation indentation to <number> spaces. This affects the indentation of lines that are wrapped or continued from the previous line.

  3. Line Breaks:

    • -nbad: Prevents line breaks after boolean and arithmetic operators.
    • -nbap: Prevents line breaks after function parameters.
    • -nbc: Prevents line breaks within function calls.

  4. Comment Formatting:

    • -c<number>: Sets the comment indentation to <number> columns.
    • -cd<number>: Sets the maximum length of comments to <number> columns. Comments exceeding this length will be wrapped.

Let's format the sample.c file using the "GNU" coding style as an example:

$ indent -gnu sample.c -o formatted_sample.c

This command applies the "GNU" coding style, adhering to the GNU coding standards.

Example output:

#include <stdio.h>

int
main ()
{
  printf ("Hello, World!\n");
  return 0;
}

As demonstrated, the indent command has formatted the code according to the "GNU" coding style, including brace placement and indentation conventions.

Explore the available options and experiment with various coding styles to identify the one that best aligns with your project's requirements and coding guidelines. Utilizing consistent coding styles contributes to more readable and maintainable codebases, which are essential for long-term project success in systemadmin and development environments.

Summary

This tutorial introduced the indent command in Linux, a tool for formatting C/C++ source code by automatically indenting it based on a defined set of rules. You learned the basic syntax and common options for customizing formatting. You then practiced using indent to format C/C++ code, including applying formatting options and customizing the output. Finally, you explored using indent to enforce specific coding styles by leveraging its configuration options. Mastering the indent command helps systemadmin professionals ensure consistent code formatting across projects, leading to improved readability and maintainability.

400+ Linux Commands