nu_command/filters/
prepend.rs

1use nu_engine::command_prelude::*;
2
3#[derive(Clone)]
4pub struct Prepend;
5
6impl Command for Prepend {
7    fn name(&self) -> &str {
8        "prepend"
9    }
10
11    fn signature(&self) -> nu_protocol::Signature {
12        Signature::build("prepend")
13            .input_output_types(vec![(Type::Any, Type::List(Box::new(Type::Any)))])
14            .required(
15                "row",
16                SyntaxShape::Any,
17                "The row, list, or table to prepend.",
18            )
19            .category(Category::Filters)
20    }
21
22    fn description(&self) -> &str {
23        "Prepend any number of rows to a table."
24    }
25
26    fn extra_description(&self) -> &str {
27        r#"Be aware that this command 'unwraps' lists passed to it. So, if you pass a variable to it,
28and you want the variable's contents to be prepended without being unwrapped, it's wise to
29pre-emptively wrap the variable in a list, like so: `prepend [$val]`. This way, `prepend` will
30only unwrap the outer list, and leave the variable's contents untouched."#
31    }
32
33    fn search_terms(&self) -> Vec<&str> {
34        vec!["add", "concatenate"]
35    }
36
37    fn examples(&self) -> Vec<Example<'_>> {
38        vec![
39            Example {
40                example: "0 | prepend [1 2 3]",
41                description: "prepend a list to an item",
42                result: Some(Value::test_list(vec![
43                    Value::test_int(1),
44                    Value::test_int(2),
45                    Value::test_int(3),
46                    Value::test_int(0),
47                ])),
48            },
49            Example {
50                example: r#""a" | prepend ["b"] "#,
51                description: "Prepend a list of strings to a string",
52                result: Some(Value::test_list(vec![
53                    Value::test_string("b"),
54                    Value::test_string("a"),
55                ])),
56            },
57            Example {
58                example: "[1 2 3 4] | prepend 0",
59                description: "Prepend one int item",
60                result: Some(Value::test_list(vec![
61                    Value::test_int(0),
62                    Value::test_int(1),
63                    Value::test_int(2),
64                    Value::test_int(3),
65                    Value::test_int(4),
66                ])),
67            },
68            Example {
69                example: "[2 3 4] | prepend [0 1]",
70                description: "Prepend two int items",
71                result: Some(Value::test_list(vec![
72                    Value::test_int(0),
73                    Value::test_int(1),
74                    Value::test_int(2),
75                    Value::test_int(3),
76                    Value::test_int(4),
77                ])),
78            },
79            Example {
80                example: "[2 nu 4 shell] | prepend [0 1 rocks]",
81                description: "Prepend ints and strings",
82                result: Some(Value::test_list(vec![
83                    Value::test_int(0),
84                    Value::test_int(1),
85                    Value::test_string("rocks"),
86                    Value::test_int(2),
87                    Value::test_string("nu"),
88                    Value::test_int(4),
89                    Value::test_string("shell"),
90                ])),
91            },
92            Example {
93                example: "[3 4] | prepend 0..2",
94                description: "Prepend a range",
95                result: Some(Value::test_list(vec![
96                    Value::test_int(0),
97                    Value::test_int(1),
98                    Value::test_int(2),
99                    Value::test_int(3),
100                    Value::test_int(4),
101                ])),
102            },
103        ]
104    }
105
106    fn run(
107        &self,
108        engine_state: &EngineState,
109        stack: &mut Stack,
110        call: &Call,
111        input: PipelineData,
112    ) -> Result<PipelineData, ShellError> {
113        let other: Value = call.req(engine_state, stack, 0)?;
114        let metadata = input.metadata();
115
116        Ok(other
117            .into_pipeline_data()
118            .into_iter()
119            .chain(input)
120            .into_pipeline_data_with_metadata(call.head, engine_state.signals().clone(), metadata))
121    }
122}
123
124#[cfg(test)]
125mod test {
126    use super::*;
127
128    #[test]
129    fn test_examples() {
130        use crate::test_examples;
131
132        test_examples(Prepend {})
133    }
134}
nu_command/filters/prepend.rs

nu_command/filters/
prepend.rs
