nu_command/platform/
is_terminal.rs

1//! OS-level TTY check for process stdio (`isatty`).
2//!
3//! Complements [`super::is_redirected`]: this command only inspects the process
4//! file descriptors. It does **not** consult Nushell pipeline destinations
5//! (`OutDest`), so it works inside `if (is-terminal)` and for scripts such as
6//! `./script.nu | cat`.
7
8use nu_engine::command_prelude::*;
9use std::io::IsTerminal as _;
10
11#[derive(Clone)]
12pub struct IsTerminal;
13
14impl Command for IsTerminal {
15    fn name(&self) -> &str {
16        "is-terminal"
17    }
18
19    fn signature(&self) -> Signature {
20        Signature::build("is-terminal")
21            .input_output_type(Type::Nothing, Type::Bool)
22            .switch("stdin", "Check if stdin is a terminal.", Some('i'))
23            .switch("stdout", "Check if stdout is a terminal.", Some('o'))
24            .switch("stderr", "Check if stderr is a terminal.", Some('e'))
25            .category(Category::Platform)
26    }
27
28    fn description(&self) -> &str {
29        "Check if the process stdin, stdout, or stderr is attached to a terminal device."
30    }
31
32    fn extra_description(&self) -> &str {
33        // Avoid substrings that collide with help completion queries (e.g. "who" in "whether").
34        "This is an operating-system level check (like bash `test -t`), not a Nushell
35pipeline check. It reports if the process file descriptor is a TTY, which is
36what scripts need for `./script.nu | cat` vs running on a terminal.
37
38To detect if a custom command's return value is piped or collected inside
39Nushell (pretty output vs structured data), use `is-redirected` instead."
40    }
41
42    fn examples(&self) -> Vec<Example<'_>> {
43        vec![
44            Example {
45                description: "Check if stdout is a terminal (default when no flag is specified).",
46                example: "is-terminal",
47                result: None,
48            },
49            Example {
50                description: r#"Return "terminal attached" if standard input is attached to a terminal, and "no terminal" if not."#,
51                example: r#"if (is-terminal --stdin) { "terminal attached" } else { "no terminal" }"#,
52                result: Some(Value::test_string("terminal attached")),
53            },
54            Example {
55                description: "Choose formatting based on process stdout being a TTY (works inside `if`).",
56                example: r#"if (is-terminal --stdout) { "human" } else { "piped" }"#,
57                result: None,
58            },
59        ]
60    }
61
62    fn search_terms(&self) -> Vec<&str> {
63        vec![
64            "input", "output", "stdin", "stdout", "stderr", "tty", "isatty",
65        ]
66    }
67
68    fn run(
69        &self,
70        engine_state: &EngineState,
71        stack: &mut Stack,
72        call: &Call,
73        _input: PipelineData,
74    ) -> Result<PipelineData, ShellError> {
75        let stdin = call.has_flag(engine_state, stack, "stdin")?;
76        let stdout = call.has_flag(engine_state, stack, "stdout")?;
77        let stderr = call.has_flag(engine_state, stack, "stderr")?;
78
79        // Default (no flags) is stdout, matching bash `test -t 1`.
80        let is_terminal = match (stdin, stdout, stderr) {
81            (true, false, false) => std::io::stdin().is_terminal(),
82            (false, false, true) => std::io::stderr().is_terminal(),
83            (false, true, false) | (false, false, false) => std::io::stdout().is_terminal(),
84            _ => {
85                return Err(ShellError::IncompatibleParametersSingle {
86                    msg: "Only one stream may be checked".into(),
87                    span: call.arguments_span(),
88                });
89            }
90        };
91
92        Ok(PipelineData::value(
93            Value::bool(is_terminal, call.head),
94            None,
95        ))
96    }
97}
nu_command/platform/is_terminal.rs

nu_command/platform/
is_terminal.rs
