Umber is a free, MIT-licensed Rust command-line tool for viewing source code and text in a terminal. Like cat, it reads files or standard input; unlike plain cat, it adds automatic language detection and syntax highlighting. Its most distinctive feature is showing otherwise invisible characters while keeping syntax highlighting intact.
What is Umber?
Umber is a terminal file viewer described by its official repository as “A modern replacement for cat with syntax highlighting and automatic language detection.” It uses tree-sitter-based highlighting and documents support for more than 100 programming languages.
It is intended for reading source code and other text files, not as a general-purpose editor. You can point it at a file or pipe text into it, then add presentation options such as line numbers, Git change indicators, themes, or a pager.
How do you install Umber?
The repository documents installation from a local checkout with Cargo. After obtaining the project source, run:
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cargo install --path .For development builds, the project documents mise install followed by mise build:debug. The cited documentation does not establish a separate package-manager or prebuilt-binary installation route, so check the repository for current distribution options.
How do you use Umber?
View a file or piped input
Give Umber a filename to display it with detected language highlighting, or pipe standard input into the command:
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umber main.rs
echo 'fn main() { println!("Hello!"); }' | umberAdd line numbers and Git change indicators
The numbers and changes style options add line numbers and Git change markers:
umber --style=numbers,changes src/main.rsShow whitespace and control characters
Use -A or --show-all to make spaces, tabs, line feeds, carriage returns, escape characters, and other controls visible while retaining syntax highlighting:
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umber -A --style=numbers problem_file.txtSelect a language, theme, or pager
Override automatic language detection with --language, choose a theme with --theme, or ask Umber to launch a pager with --pager:
umber --language json response.log
umber --theme nord config.yaml
umber --pager Cargo.tomlChoose richer highlighting
The --style=rich option enables richer highlighting. Markdown enables this style automatically. The README warns that rich highlighting can be significantly slower on very large files, so use the simpler style when processing speed matters more than the extra presentation.
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How is Umber different from bat?
Both tools add syntax-aware display to the familiar file-viewing role of cat. The comparison below reflects the claims and features documented in Umber’s README; it is not a performance benchmark or a full feature audit of both projects.
| Area | Umber | bat, as characterized in Umber’s README |
|---|---|---|
| Highlighting | Tree-sitter-based syntax highlighting; supports 100+ programming languages. | Umber’s README identifies bat as another syntax-highlighting cat replacement but does not specify its highlighting engine or language count. |
| Language detection | Automatic detection, with a --language option to specify a language. |
Not stated in the cited comparison. |
| Line and Git decoration | Optional line numbers and Git change indicators through styles. | Not stated in the cited comparison. |
| Unprintable characters | -A/--show-all reveals control and whitespace characters while preserving syntax highlighting. |
Umber’s README says bat’s -A mode does not maintain full syntax highlighting while showing unprintable characters. |
| Stdin and pager | Accepts standard input and can launch a pager. | Not stated in the cited comparison. |
| Themes and completions | Supports themes and documents completions for Bash, Zsh, Fish, and PowerShell. | Not stated in the cited comparison. |
| Binary-file handling | The README comparison does not establish binary-file detection. | Umber’s README suggests bat when binary-file detection is needed. |
The practical distinction to consider is visible-character inspection: Umber’s README claims it can reveal unprintable characters without dropping syntax highlighting. If binary-file detection is the priority, that same README points readers toward bat. The cited sources provide no reliable benchmark comparing speed or large-file performance between the two tools.
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Does Umber support shell completions?
The README documents completion generation for Bash, Zsh, Fish, and PowerShell. For example, its Bash command writes the generated completion file to the conventional user-local location:
umber --completions bash > ~/.local/share/bash-completion/completions/umberUse the corresponding shell name with --completions for the other supported shells, and follow the completion installation conventions for your shell environment.
Quick Recap
When should you use Umber?
- Use it when you want source code or text displayed with automatic language detection and syntax highlighting.
- Choose
-Awhen diagnosing whitespace or control-character problems and you still want syntax highlighting. - Use
--style=numbers,changeswhen line references and Git change markers help with review. - Consider another tool, such as bat per Umber’s README, when binary-file detection is important.
- For very large files, avoid rich highlighting if its documented performance cost is a concern.
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