127 lines
5.6 KiB
Markdown
127 lines
5.6 KiB
Markdown
---
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obj: application
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repo: https://github.com/fornwall/rust-script
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website: https://rust-script.org
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---
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# RustScript
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With rust-script Rust files and expressions can be executed just like a shell or Python script. Features include:
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- Caching compiled artifacts for speed.
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- Reading Cargo manifests embedded in Rust scripts.
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- Supporting executable Rust scripts via Unix shebangs and Windows file associations.
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- Using expressions as stream filters (i.e. for use in command pipelines).
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- Running unit tests and benchmarks from scripts.
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## Scripts
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The primary use for rust-script is for running Rust source files as scripts. For example:
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```
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$ echo 'println!("Hello, World!");' > hello.rs
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$ rust-script hello.rs
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Hello, World!
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```
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Under the hood, a Cargo project will be generated and built (with the Cargo output hidden unless compilation fails or the `-c/--cargo-output` option is used). The first invocation of the script will be slower as the script is compiled - subsequent invocations of unmodified scripts will be fast as the built executable is cached.
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As seen from the above example, using a `fn main() {}` function is not required. If not present, the script file will be wrapped in a `fn main() { ... }` block.
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rust-script will look for embedded dependency and manifest information in the script as shown by the below two equivalent `now.rs` variants:
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```rust
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#!/usr/bin/env rust-script
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//! This is a regular crate doc comment, but it also contains a partial
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//! Cargo manifest. Note the use of a *fenced* code block, and the
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//! `cargo` "language".
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//!
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//! ```cargo
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//! [dependencies]
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//! time = "0.1.25"
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//! ```
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fn main() {
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println!("{}", time::now().rfc822z());
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}
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```
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```rust
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// cargo-deps: time="0.1.25"
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// You can also leave off the version number, in which case, it's assumed
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// to be "*". Also, the `cargo-deps` comment *must* be a single-line
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// comment, and it *must* be the first thing in the file, after the
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// shebang.
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// Multiple dependencies should be separated by commas:
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// cargo-deps: time="0.1.25", libc="0.2.5"
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fn main() {
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println!("{}", time::now().rfc822z());
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}
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```
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The output from running one of the above scripts may look something like:
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```
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$ rust-script now
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Wed, 28 Oct 2020 00:38:45 +0100
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```
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## Useful command-line arguments:
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- `--bench`: Compile and run benchmarks. Requires a nightly toolchain.
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- `--debug`: Build a debug executable, not an optimised one.
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- `--force`: Force the script to be rebuilt. Useful if you want to force a recompile with a different toolchain.
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- `--package`: Generate the Cargo package and print the path to it - but don’t compile or run it. Effectively “unpacks” the script into a Cargo package.
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- `--test`: Compile and run tests.
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- `--wrapper`: Add a wrapper around the executable. Can be used to run debugging with e.g. `rust-script --debug --wrapper rust-lldb my-script.rs` or benchmarking with `rust-script --wrapper "hyperfine --runs 100" my-script.rs`
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## Executable Scripts
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On Unix systems, you can use `#!/usr/bin/env rust-script` as a shebang line in a Rust script. This will allow you to execute a script files (which don’t need to have the `.rs` file extension) directly.
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If you are using Windows, you can associate the `.ers` extension (executable Rust - a renamed `.rs` file) with rust-script. This allows you to execute Rust scripts simply by naming them like any other executable or script.
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This can be done using the `rust-script --install-file-association` command. Uninstall the file association with `rust-script --uninstall-file-association`.
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If you want to make a script usable across platforms, use both a shebang line and give the file a `.ers` file extension.
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## Expressions
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Using the `-e/--expr` option a Rust expression can be evaluated directly, with dependencies (if any) added using `-d/--dep`:
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```
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$ rust-script -e '1+2'
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3
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$ rust-script --dep time --expr "time::OffsetDateTime::now_utc().format(time::Format::Rfc3339).to_string()"`
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"2020-10-28T11:42:10+00:00"
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$ # Use a specific version of the time crate (instead of default latest):
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$ rust-script --dep time=0.1.38 -e "time::now().rfc822z().to_string()"
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"2020-10-28T11:42:10+00:00"
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```
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The code given is embedded into a block expression, evaluated, and printed out using the Debug formatter (i.e. `{:?}`).
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## Filters
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You can use rust-script to write a quick filter, by specifying a closure to be called for each line read from stdin, like so:
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```
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$ cat now.ers | rust-script --loop \
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"let mut n=0; move |l| {n+=1; println!(\"{:>6}: {}\",n,l.trim_end())}"
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1: // cargo-deps: time="0.1.25"
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3: fn main() {
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4: println!("{}", time::now().rfc822z());
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5: }
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```
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You can achieve a similar effect to the above by using the `--count` flag, which causes the line number to be passed as a second argument to your closure:
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```
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$ cat now.ers | rust-script --count --loop \
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"|l,n| println!(\"{:>6}: {}\", n, l.trim_end())"
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1: // cargo-deps: time="0.1.25"
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2: fn main() {
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3: println!("{}", time::now().rfc822z());
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4: }
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```
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## Environment Variables
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The following environment variables are provided to scripts by rust-script:
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- `$RUST_SCRIPT_BASE_PATH`: the base path used by rust-script to resolve relative dependency paths. Note that this is not necessarily the same as either the working directory, or the directory in which the script is being compiled.
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- `$RUST_SCRIPT_PKG_NAME`: the generated package name of the script.
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- `$RUST_SCRIPT_SAFE_NAME`: the file name of the script (sans file extension) being run. For scripts, this is derived from the script’s filename. May also be `expr` or `loop` for those invocations.
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- `$RUST_SCRIPT_PATH`: absolute path to the script being run, assuming one exists. Set to the empty string for expressions.
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