How to manually adjust the indentation of a selected region in Emacs: Using indent-rigidly

When editing code or text in Emacs, you may want to shift multiple lines of indentation to the right or left at once.

The Emacs standard command indent-rigidly is useful for this.

This article introduces how to manually adjust the indentation of a selected range and how to finish the operation after adjustment.

1. What is indent-rigidly?

indent-rigidly is a command that changes the indentation of a selected region at once.

While the regular indent-region automatically adjusts the indentation according to the syntax of the programming language, indent-rigidly allows you to manually move the indentation left or right while preserving the relative indentation of each line.

For example, consider the following code:

if condition:
    print("Hello")
    print("World")

If you shift these three lines to the right by 4 characters, it will look like this:

    if condition:
        print("Hello")
        print("World")

The key feature is that the relative indentation of each line is maintained.

2. Manually Adjusting the Indentation of a Selected Range

The steps are as follows:

1. Start range selection with C-SPC.
2. Move the cursor to select the target lines.
3. Execute indent-rigidly with C-x TAB.
4. Adjust the indentation with the left and right arrow keys.

After executing indent-rigidly, you can adjust it with the following keys:

S-→ and S-← are performed by pressing the Shift key while pressing the left and right arrow keys.

Note: The interactive adjustment with the arrow keys may behave differently depending on the Emacs version and settings.

3. How to End Indentation Adjustment?

After executing C-x TAB and interactively adjusting the indentation, press RET (Enter key) to confirm the adjustment and exit.

The basic flow is as follows:

C-SPC      Start range selection
Cursor movement  Select the range
C-x TAB    Execute indent-rigidly
→ → →      Move 3 characters to the right
RET        Confirm the adjustment and exit

If you want to interrupt the operation, use C-g.

However, pressing C-g does not necessarily automatically revert the indentation changes made up to that point.

If you want to undo the changes, use undo (usually C-/) as needed.

4. Changing Indentation by a Specified Number of Characters

In addition to interactive adjustment, you can also specify a number to change the indentation at once.

To shift 4 characters to the right:

C-u 4 C-x TAB

To shift 4 characters to the left:

C-u - 4 C-x TAB

This is useful when you know the number of characters you want to change.

5. Difference from indent-region

Emacs has another command for adjusting indentation called indent-region.

For example, if you want to format code such as Python or C according to the syntax, indent-region is suitable.

On the other hand, if you want to move multiple lines to the right or left without changing the code structure, indent-rigidly is useful.

Summary

To manually adjust the indentation of a selected range in Emacs, use indent-rigidly.

The operations to remember are as follows:

The most important thing to remember is to start adjusting with C-x TAB and end with RET.

It is useful when you want to make fine manual adjustments to the indentation of multiple lines.