Snippet execution

Executing code blocks

Annotating a code block with a +exec attribute will make it executable. Pressing control+e when viewing a slide that contains an executable block, the code in the snippet will be executed and the output of the execution will be displayed on a box below it. The code execution is stateful so if you switch to another slide and then go back, you will still see the output.

```bash +exec
echo hello world
```

Code execution must be explicitly enabled by using either:

• The -x command line parameter when running presenterm.
• Setting the snippet.exec.enable property to true in your presenterm config file.

Refer to the table in the highlighting page for the list of languages for which code execution is supported.

Output placing

By default a snippet's output will always show up right below the snippet. However, if you wanted to show the output in a different place in a slide (e.g. another column) or even in another slide you can do this by:

1. Defining a snippet's identifier:

```bash +exec +id:foo
echo hellow world
```

2. Referencing that identifier where you want the output to appear by using the snippet_output comment command:

<!-- snippet_output: foo -->

A single snippet can be referenced multiple times in multiple slides, as long as the slide you're referencing it in comes after the snippet. The snippet will only be executed once, and every snippet_output command will display that single execution's output.

Validating snippets

While you're developing your presentation you probably want to make sure the executable snippets you write in it are correct and don't contain any syntax errors. While you can do this by constantly pressing <c-e> every time you change a snippet, this is automatically done by presenterm if you pass in the --validate-snippets flag.

When you pass in this flag, presenterm will:

• Automatically run all +exec, +exec_replace, and +validate snippets as soon as your presentation starts. Note that the +validate flag is a special one that doesn't make a snippet executable but still validates it by running it during development.
• Report an error if any of the snippets returns an exit code other than 0.
• Re-run all snippets +exec and +exec_repalce snippets every time the presentation is reloaded.

In case you expect a snippet to return an exit code other than 0, you can use the +expect:failure flag. This will cause presenterm to display an error if the snippet does not fail.

For example, the following defines a snippet that's not executable but that will be validated if --validate-snippets is passed in and will display an error if the snippet does not fail.

fn main() {
    let q = 42;
    let w = q + "foo"; // oops
}

Executing and replacing

Similar to +exec, +exec_replace causes a snippet to be executable but:

• Execution happens automatically without user intervention.
• The snippet will be automatically replaced with its execution output.

This can be useful to run programs that generate some form of ASCII art that you'd like to generate dynamically.

Because of the risk involved in +exec_replace, where code gets automatically executed when running a presentation, this requires users to explicitly opt in to it. This can be done by either passing in the -X command line parameter or setting the snippet.exec_replace.enable flag in your configuration file to true.

Alternative executors

Some languages support alternative executors. For example, rust code can be ran via rust-script, which allows you to use external crates. These executors can be used by specifying :<executor-name> after +exec or +exec_replace.

For example, the following rust snippet will be executed using rust-script:

```rust +exec:rust-script
# //! ```cargo
# //! [dependencies]
# //! time = "0.1.25"
# //! ```
# // The lines above will be hidden
fn main() {
    println!("the time is {}", time::now().rfc822z());
}
```

The supported alternative executors are:

• rust-script for rust snippets.
• pytest and uv for python snippets.

Code to image conversions

The +image attribute behaves like +exec_replace but also assumes the output of the executed snippet will be an image, and it will render it as such. For this to work, the code must only emit an image in jpg/png formats and nothing else.

For example, this would render the demo presentation's image:

```bash +image
cat examples/doge.png
```

This attribute carries the same risks as +exec_replace and therefore needs to be enabled via the same flags.

Executing snippets that need a TTY

If you're trying to execute a program like top that needs to run on a TTY as it renders text, clears the screen, etc, you can use the +acquire_terminal modifier on a code already marked as executable with +exec. Executing snippets tagged with these two attributes will cause presenterm to suspend execution, the snippet will be invoked giving it the raw terminal to do whatever it needs, and upon its completion presenterm will resume its execution.

Styled execution output

Snippets that generate output which contains escape codes that change the colors or styling of the text will be parsed and displayed respecting those styles. Do note that you may need to force certain tools to use colored output as they will likely not use it by default.

For example, to get colored output when invoking ls you can use:

```bash +exec
ls /tmp --color=always
```

The parameter or way to enable this will depend on the tool being invoked.

Hiding code lines

When you mark a code snippet as executable via the +exec flag, you may not be interested in showing all the lines to your audience, as some of them may not be necessary to convey your point. For example, you may want to hide imports, non-essential functions, initialization of certain variables, etc. For this purpose, presenterm supports a prefix under certain programming languages that let you indicate a line should be executed when running the code but should not be displayed in the presentation.

For example, in the following code snippet only the print statement will be displayed but the entire snippet will be ran:

```rust
# fn main() {
println!("Hello world!");
# }
```

Rather than blindly relying on a prefix that may have a meaning in a language, prefixes are chosen on a per language basis. The languages that are supported and their prefix is:

• rust: # .
• python/bash/fish/shell/zsh/kotlin/java/javascript/typescript/c/c++/go: /// .

This means that any line in a rust code snippet that starts with # will be hidden, whereas all lines in, say, a golang code snippet that starts with a /// will be hidden.

Pre-rendering

Some languages support pre-rendering. This means the code block is transformed into something else when the presentation is loaded. The languages that currently support this are mermaid, LaTeX, and typst where the contents of the code block is transformed into an image, allowing you to define formulas as text in your presentation. This can be done by using the +render attribute on a code block.

See the LaTeX and typst, mermaid, and d2 docs for more information.