1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164

use clap::Parser;
use rustutils_runnable::Runnable;
use std::env;
use std::error::Error;
use std::ffi::{OsStr, OsString};
use std::io::Write;
use std::os::unix::ffi::OsStrExt;
use std::process::{Command, ExitStatus};

/// Set environment variables and run command.
///
/// When no command is supplied, print the current environment variables.
#[derive(Parser, Clone, Debug)]
#[clap(author, version, about, long_about = None)]
pub struct Env {
    /// Start with an empty environment.
    #[clap(short, long)]
    ignore_environment: bool,
    /// When printing the current environment, separate the variables with a NUL character.
    #[clap(short = '0', long)]
    null: bool,
    /// When printing the current environment, output it as JSON.
    #[clap(short, long, conflicts_with = "null")]
    json: bool,
    /// Unset variables.
    #[clap(short, long)]
    unset: Vec<OsString>,
    /// Environment variables to set, in the shape of `NAME=value`.
    variables: Vec<OsString>,
    /// Command to run, using the specified environment.
    #[clap(last = true)]
    command: Vec<OsString>,
}

/// Parse an environment variable definition.
///
/// Environment variables are specified in the form `VARIABLE=value`. Typically, the variables are
/// uppercased, but this is not mandatory.
pub fn parse_variable(var: &OsStr) -> Option<(&OsStr, &OsStr)> {
    let var = var.as_bytes();
    var.iter()
        .enumerate()
        .skip(1)
        .filter(|(_index, byte)| **byte == b'=')
        .map(|(index, _byte)| index)
        .last()
        .map(|pos| {
            (
                OsStr::from_bytes(&var[..pos]),
                OsStr::from_bytes(&var[pos + 1..]),
            )
        })
}

#[test]
fn can_parse_variable() {
    assert_eq!(parse_variable(OsStr::from_bytes(b"")), None);
    assert_eq!(parse_variable(OsStr::from_bytes(b"=")), None);
    assert_eq!(parse_variable(OsStr::from_bytes(b"VAR")), None);
    assert_eq!(parse_variable(OsStr::from_bytes(b"=VAR")), None);
    assert_eq!(
        parse_variable(OsStr::from_bytes(b"VAR=value")),
        Some((OsStr::from_bytes(b"VAR"), OsStr::from_bytes(b"value")))
    );
    assert_eq!(
        parse_variable(OsStr::from_bytes(b"VAR=")),
        Some((OsStr::from_bytes(b"VAR"), OsStr::from_bytes(b"")))
    );
}

impl Env {
    /// Setup environment
    pub fn setup(&self) {
        // unset every environment variable
        if self.ignore_environment {
            for (name, _) in env::vars_os() {
                env::remove_var(name);
            }
        }

        // unset request environment variables
        for variable in &self.unset {
            env::remove_var(variable);
        }
    }

    pub fn parse_arguments(&self) -> Result<usize, Box<dyn Error>> {
        let count = self
            .variables
            .iter()
            .map(|variable| parse_variable(variable))
            .take_while(|parsed| parsed.is_some())
            .filter_map(|parsed| parsed)
            .inspect(|(name, value)| env::set_var(name, value))
            .count();
        Ok(count)
    }

    pub fn run_command(&self, offset: usize) -> Result<Option<ExitStatus>, Box<dyn Error>> {
        let mut args = self
            .variables
            .iter()
            .skip(offset)
            .chain(self.command.iter());
        if let Some(arg) = args.next() {
            let mut command = Command::new(arg);
            let result = command.args(args).spawn()?.wait()?;
            Ok(Some(result))
        } else {
            Ok(None)
        }
    }

    pub fn run(&self) -> Result<Option<ExitStatus>, Box<dyn Error>> {
        self.setup();
        let offset = self.parse_arguments()?;
        let result = self.run_command(offset)?;
        if result.is_none() {
            self.show()?;
        }
        Ok(result)
    }

    pub fn show(&self) -> Result<(), Box<dyn Error>> {
        if self.json {
            self.show_json()
        } else {
            let separator = match self.null {
                true => OsStr::new("\0"),
                false => OsStr::new("\n"),
            };
            self.show_normal(separator)
        }
    }

    pub fn show_json(&self) -> Result<(), Box<dyn Error>> {
        let mut environment: std::collections::BTreeMap<String, String> = Default::default();
        for (name, value) in env::vars_os() {
            if let (Some(name), Some(value)) = (name.to_str(), value.to_str()) {
                environment.insert(name.to_string(), value.to_string());
            }
        }
        let mut stdout = std::io::stdout();
        stdout.write_all(serde_json::to_string(&environment)?.as_bytes())?;
        Ok(())
    }
    pub fn show_normal(&self, separator: &OsStr) -> Result<(), Box<dyn Error>> {
        let mut stdout = std::io::stdout();
        for (name, value) in env::vars_os() {
            stdout.write_all(name.as_bytes())?;
            stdout.write_all(b"=")?;
            stdout.write_all(value.as_bytes())?;
            stdout.write_all(separator.as_bytes())?;
        }
        Ok(())
    }
}

impl Runnable for Env {
    fn run(&self) -> Result<(), Box<dyn Error>> {
        self.run()?;
        Ok(())
    }
}