130 lines
4.9 KiB
Markdown
130 lines
4.9 KiB
Markdown
# shed
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A Unix shell written in Rust. The name is a nod to the two oldest Unix utilities — `sh` and `ed` — reflecting the shell's emphasis on a capable built-in line editor alongside standard shell functionality.
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## Features
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### Line Editor
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shed includes a built-in vim emulator as its line editor, written from scratch — not a readline wrapper or external library. It aims to provide a more precise vim editing experience at the shell prompt.
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- **Normal mode** — motions (`w`, `b`, `e`, `f`, `t`, `%`, `0`, `$`, etc.), verbs (`d`, `c`, `y`, `p`, `r`, `x`, `~`, etc.), text objects (`iw`, `aw`, `i"`, `a{`, `is`, etc.), registers, `.` repeat, `;`/`,` repeat, and counts
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- **Insert mode** — insert, append, replace, with Ctrl+W word deletion and undo/redo
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- **Visual mode** — character-wise selection with operator support
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- **Real-time syntax highlighting** — commands, keywords, strings, variables, redirections, and operators are colored as you type
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- **Tab completion** — context-aware completion for commands, file paths, and variables
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### Prompt
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The prompt string supports escape sequences for dynamic content:
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| Escape | Description |
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|--------|-------------|
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| `\u` | Username |
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| `\h`, `\H` | Hostname (short / full) |
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| `\w`, `\W` | Working directory (full / basename, truncation configurable via `shopt`) |
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| `\$` | `$` for normal users, `#` for root |
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| `\t`, `\T` | Last command runtime (milliseconds / human-readable) |
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| `\s` | Shell name |
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| `\e[...` | ANSI escape sequences for colors and styling |
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| `\!name` | Execute a shell function and embed its output |
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The `\!` escape is particularly useful — it lets you embed the output of any shell function directly in your prompt. Define a function that prints something, then reference it in your prompt string:
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```sh
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gitbranch() { git branch --show-current 2>/dev/null; }
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export PS1='\u@\h \W \!gitbranch \$ '
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```
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Additionally, `echo` now has a `-p` flag that expands prompt escape sequences, similar to how the `-e` flag expands conventional escape sequences.
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### Shell Language
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shed's scripting language contains all of the essentials.
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- **Control flow** — `if`/`elif`/`else`, `for`, `while`, `until`, `case` with pattern matching and fallthrough
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- **Functions** — user-defined with local variable scoping, recursion depth limits, and `return`
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- **Pipes and redirections** — `|`, `|&` (pipe stderr), `<`, `>`, `>>`, `<<` (heredoc), `<<<` (herestring), fd duplication (`2>&1`)
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- **Process substitution** — `<(...)` and `>(...)`
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- **Command substitution** — `$(...)` and backticks
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- **Arithmetic expansion** — `$((...))` with `+`, `-`, `*`, `/`, `%`, `**`
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- **Parameter expansion** — `${var}`, `${var:-default}`, `${var:=default}`, `${var:+alt}`, `${var:?err}`, `${#var}`, `${var#pattern}`, `${var%pattern}`, `${var/pat/rep}`
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- **Brace expansion** — `{a,b,c}`, `{1..10}`, `{1..10..2}`
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- **Glob expansion** — `*`, `?`, `[...]` with optional dotglob
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- **Tilde expansion** — `~` and `~user`
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- **Logical operators** — `&&`, `||`, `&` (background)
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- **Test expressions** — `[[ ... ]]` with file tests, string comparison, arithmetic comparison, and regex matching
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- **Subshells** — `(...)` for isolated execution
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- **Variable attributes** — `export`, `local`, `readonly`
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### Job Control
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- Background execution with `&`
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- Suspend foreground jobs with Ctrl+Z
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- `fg`, `bg`, `jobs`, `disown` with flags (`-l`, `-p`, `-r`, `-s`, `-h`, `-a`)
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- Process group management and proper signal forwarding
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### Builtins
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`echo`, `cd`, `pwd`, `read`, `export`, `local`, `readonly`, `unset`, `source`, `eval`, `exec`, `shift`, `alias`, `unalias`, `trap`, `jobs`, `fg`, `bg`, `disown`, `pushd`, `popd`, `dirs`, `shopt`, `builtin`, `command`, `return`, `break`, `continue`, `exit`, `true`, `false`, `:`
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### Configuration
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Shell options are managed through `shopt`:
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```sh
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shopt core.autocd=true # cd by typing a directory path
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shopt core.dotglob=true # include hidden files in globs
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shopt prompt.highlight=false # toggle syntax highlighting
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shopt prompt.edit_mode=vi # editor mode
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shopt core.max_hist=5000 # history size
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```
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The rc file is loaded from `~/.shedrc` on startup.
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## Building
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### Cargo
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Requires Rust (edition 2024).
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```sh
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cargo build --release
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```
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The binary will be at `target/release/shed`.
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### Nix
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A flake is provided with a NixOS module and a Home Manager module.
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```sh
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# Build and run directly
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nix run github:km-clay/shed
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# Or add to your flake inputs
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inputs.shed.url = "github:km-clay/shed";
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```
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To use the NixOS module:
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```nix
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# flake.nix outputs
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nixosConfigurations.myhost = nixpkgs.lib.nixosSystem {
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modules = [
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shed.nixosModules.shed
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# ...
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];
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};
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```
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Or with Home Manager:
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```nix
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imports = [ shed.homeModules.shed ];
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```
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## Status
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`shed` is experimental software and is currently under active development. It covers most day-to-day interactive shell usage and a good portion of POSIX shell scripting, but it is not yet fully POSIX-compliant.
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