nu_command/filters/
length.rs

1#[cfg(feature = "sqlite")]
2use crate::database::QueryPlan;
3use nu_engine::command_prelude::*;
4use std::io::Read;
5
6#[derive(Clone)]
7pub struct Length;
8
9impl Command for Length {
10    fn name(&self) -> &str {
11        "length"
12    }
13
14    fn description(&self) -> &str {
15        "Count the number of items in an input list, rows in a table, or bytes in binary data."
16    }
17
18    fn signature(&self) -> nu_protocol::Signature {
19        Signature::build("length")
20            .input_output_types(vec![
21                (Type::List(Box::new(Type::Any)), Type::Int),
22                (Type::Binary, Type::Int),
23                (Type::Nothing, Type::Int),
24                #[cfg(feature = "sqlite")]
25                (Type::Custom("SQLiteQueryBuilder".into()), Type::Int),
26            ])
27            .allow_variants_without_examples(true)
28            .category(Category::Filters)
29    }
30
31    fn search_terms(&self) -> Vec<&str> {
32        vec!["count", "size", "wc"]
33    }
34
35    fn run(
36        &self,
37        _engine_state: &EngineState,
38        _stack: &mut Stack,
39        call: &Call,
40        input: PipelineData,
41    ) -> Result<PipelineData, ShellError> {
42        length_row(call, input)
43    }
44
45    fn examples(&self) -> Vec<Example<'_>> {
46        vec![
47            Example {
48                description: "Count the number of items in a list",
49                example: "[1 2 3 4 5] | length",
50                result: Some(Value::test_int(5)),
51            },
52            Example {
53                description: "Count the number of rows in a table",
54                example: "[{a:1 b:2}, {a:2 b:3}] | length",
55                result: Some(Value::test_int(2)),
56            },
57            Example {
58                description: "Count the number of bytes in binary data",
59                example: "0x[01 02] | length",
60                result: Some(Value::test_int(2)),
61            },
62            Example {
63                description: "Count the length a null value",
64                example: "null | length",
65                result: Some(Value::test_int(0)),
66            },
67        ]
68    }
69}
70
71fn length_row(call: &Call, input: PipelineData) -> Result<PipelineData, ShellError> {
72    let span = input.span().unwrap_or(call.head);
73
74    #[cfg(feature = "sqlite")]
75    // Pushdown optimization: handle 'length' via QueryPlan using COUNT(*)
76    if let PipelineData::Value(Value::Custom { val, .. }, ..) = &input
77        && let Some(plan) = QueryPlan::try_from_any(val.as_any())
78    {
79        let count = plan.count(call.head)?;
80        return Ok(Value::int(count, call.head).into_pipeline_data());
81    }
82
83    match input {
84        PipelineData::Empty | PipelineData::Value(Value::Nothing { .. }, ..) => {
85            Ok(Value::int(0, call.head).into_pipeline_data())
86        }
87        PipelineData::Value(Value::Binary { val, .. }, ..) => {
88            Ok(Value::int(val.len() as i64, call.head).into_pipeline_data())
89        }
90        #[cfg(feature = "sqlite")]
91        PipelineData::Value(
92            Value::Custom {
93                val, internal_span, ..
94            },
95            ..,
96        ) => Err(ShellError::OnlySupportsThisInputType {
97            exp_input_type: "list, table, binary, and nothing".into(),
98            wrong_type: val.type_name(),
99            dst_span: call.head,
100            src_span: internal_span,
101        }),
102        PipelineData::Value(Value::List { vals, .. }, ..) => {
103            Ok(Value::int(vals.len() as i64, call.head).into_pipeline_data())
104        }
105        PipelineData::ListStream(stream, ..) => {
106            Ok(Value::int(stream.into_iter().count() as i64, call.head).into_pipeline_data())
107        }
108        PipelineData::ByteStream(stream, ..) if stream.type_().is_binary_coercible() => {
109            Ok(Value::int(
110                match stream.reader() {
111                    Some(r) => r.bytes().count() as i64,
112                    None => 0,
113                },
114                call.head,
115            )
116            .into_pipeline_data())
117        }
118        _ => Err(ShellError::OnlySupportsThisInputType {
119            exp_input_type: "list, table, binary, and nothing".into(),
120            wrong_type: input.get_type().to_string(),
121            dst_span: call.head,
122            src_span: span,
123        }),
124    }
125}
126
127#[cfg(test)]
128mod test {
129    use super::*;
130
131    #[test]
132    fn test_examples() -> nu_test_support::Result {
133        nu_test_support::test().examples(Length)
134    }
135}
nu_command/filters/length.rs

nu_command/filters/
length.rs
