Screenshots or Visual Evidence

Oct 13, 2025 by wbrum.org 144 views

Introduction

The Fish shell is a popular command-line shell known for its user-friendly interface and efficient syntax highlighting feature. However, a recent issue has been reported where the syntax highlighting feature incorrectly applies underline formatting to trailing spaces after a command. This behavior is unexpected and visually distracting, as trailing spaces should not inherit the underline formatting of the command. In this article, we will delve into the steps to reproduce this issue, the expected behavior, the actual behavior, and provide a solution to this problem.

Description

The Fish shell syntax highlighting feature is designed to enhance the readability of commands and their output. However, when the fish_color_command variable is set to apply an underline, the trailing spaces after a command are also underlined, which is incorrect. Trailing spaces should not be underlined, as they do not carry any significant meaning in the context of the command.

Steps to Reproduce

To reproduce this issue, follow these steps:

Step 1: Open a Terminal with Fish Shell

Open a terminal on your system and ensure that the Fish shell is installed and set as the default shell.

Step 2: Set Command Formatting to Include Underline

Run the following command to set the command formatting to include an underline:

set -U fish_color_command --underline

This will apply an underline to all commands in the Fish shell.

Step 3: Type a Command with Trailing Spaces

Type a command followed by one or more spaces, but do not press Enter. For example:

ls<space><space>

This will display the command with trailing spaces.

Step 4: Observe Syntax Highlighting Behavior

Observe the syntax highlighting behavior on the command and the trailing spaces. You should notice that the trailing spaces are also underlined, which is incorrect.

Expected Behavior

The expected behavior is that the command (ls in the example) should be underlined, but the trailing spaces after the command should not be underlined. They should remain unformatted (default terminal appearance).

Actual Behavior

The actual behavior is that the command (ls in the example) is underlined, as expected. However, the trailing spaces after the command are also underlined, which is incorrect and visually distracting.

Screenshots or Visual Evidence

To illustrate this issue, a screenshot of the Fish shell terminal displaying the command with trailing spaces and underline formatting is provided below:

Solution

To resolve this issue, you can modify the fish_color_command variable to exclude trailing spaces from the underline formatting. You can do this by setting the fish_color_command variable to apply an underline only to the command itself, without including trailing spaces. Here's an example:

set -U fish_color_command --underline --bold

This will apply an underline and bold formatting to the command itself, without including trailing spaces.

Alternatively, you can also use the fish_color_trailing variable to set the formatting for trailing spaces. By default, trailing spaces are not underlined. However, if you want to customize the formatting for trailing spaces, you can set the fish_color_trailing variable to apply a specific formatting, such as a different color or font style.

Conclusion

Introduction

In our previous article, we discussed the issue of Fish shell syntax highlighting incorrectly applying underline formatting to trailing spaces after a command. In this article, we will provide a Q&A section to address common questions and concerns related to this issue.

Q: What is the cause of this issue?

A: The cause of this issue is due to the way the Fish shell syntax highlighting feature is implemented. When the fish_color_command variable is set to apply an underline, the trailing spaces after a command are also underlined, which is incorrect.

Q: How can I reproduce this issue?

A: To reproduce this issue, follow these steps:

Open a terminal with Fish shell.
Set the command formatting to include an underline by running the following command: set -U fish_color_command --underline
Type a command followed by one or more spaces, but do not press Enter. For example: ls<space><space>
Observe the syntax highlighting behavior on the command and the trailing spaces.

Q: What is the expected behavior?

A: The expected behavior is that the command (ls in the example) should be underlined, but the trailing spaces after the command should not be underlined. They should remain unformatted (default terminal appearance).

Q: What is the actual behavior?

A: The actual behavior is that the command (ls in the example) is underlined, as expected. However, the trailing spaces after the command are also underlined, which is incorrect and visually distracting.

Q: How can I fix this issue?

A: To fix this issue, you can modify the fish_color_command variable to exclude trailing spaces from the underline formatting. You can do this by setting the fish_color_command variable to apply an underline only to the command itself, without including trailing spaces. Here's an example: set -U fish_color_command --underline --bold

Q: Is this issue specific to Fish shell?

A: No, this issue is not specific to Fish shell. Other shells, such as Bash and Zsh, may also exhibit similar behavior.

Q: Can I customize the syntax highlighting feature in Fish shell?

A: Yes, you can customize the syntax highlighting feature in Fish shell by modifying the fish_color_command and fish_color_trailing variables. You can also use other variables, such as fish_color_prompt, to customize the appearance of the command prompt.

Q: Where can I find more information about Fish shell syntax highlighting?

A: You can find more information about Fish shell syntax highlighting in the official Fish shell documentation. Additionally, you can search online for tutorials and guides on customizing the syntax highlighting feature in Fish shell.

Conclusion

In conclusion, the Fish shell syntax highlighting feature incorrectly applies underline formatting to trailing spaces after a command. By following the steps outlined in this article, you can reproduce this issue and understand the expected and actual behavior. Additionally, you can modify the fish_color_command variable to exclude trailing spaces from the underline formatting or use the fish_color_trailing variable to customize the formatting for trailing spaces.