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rexpect

Documentation License Crates Status

Spawn, control, and respond to expected patterns of child applications and processes, enabling the automation of interactions and testing. Components include:

  • session: start a new process and interact with it; primary module of rexpect.
  • reader: non-blocking reader, which supports waiting for strings, regex, and EOF.
  • process: spawn a process in a pty.

The goal is to offer a similar set of functionality as pexpect.

Examples

For more examples, check the examples directory.

Basic usage

Simple example for interacting via ftp:

use rexpect::spawn;
use rexpect::error::*;

fn do_ftp() -> Result<(), Error> {
    let mut p = spawn("ftp speedtest.tele2.net", Some(30_000))?;
    p.exp_regex("Name \\(.*\\):")?;
    p.send_line("anonymous")?;
    p.exp_string("Password")?;
    p.send_line("test")?;
    p.exp_string("ftp>")?;
    p.send_line("cd upload")?;
    p.exp_string("successfully changed.\r\nftp>")?;
    p.send_line("pwd")?;
    p.exp_regex("[0-9]+ \"/upload\"")?;
    p.send_line("exit")?;
    p.exp_eof()?;
    Ok(())
}

fn main() {
    do_ftp().unwrap_or_else(|e| panic!("ftp job failed with {}", e));
}

Example with bash and reading from programs

use rexpect::spawn_bash;
use rexpect::error::*;

fn do_bash() -> Result<(), Error> {
    let mut p = spawn_bash(Some(2000))?;

    // case 1: wait until program is done
    p.send_line("hostname")?;
    let hostname = p.read_line()?;
    p.wait_for_prompt()?; // go sure `hostname` is really done
    println!("Current hostname: {}", hostname);

    // case 2: wait until done, only extract a few infos
    p.send_line("wc /etc/passwd")?;
    // `exp_regex` returns both string-before-match and match itself, discard first
    let (_, lines) = p.exp_regex("[0-9]+")?;
    let (_, words) = p.exp_regex("[0-9]+")?;
    let (_, bytes) = p.exp_regex("[0-9]+")?;
    p.wait_for_prompt()?; // go sure `wc` is really done
    println!("/etc/passwd has {} lines, {} words, {} chars", lines, words, bytes);

    // case 3: read while program is still executing
    p.execute("ping 8.8.8.8", "bytes of data")?; // returns when it sees "bytes of data" in output
    for _ in 0..5 {
        // times out if one ping takes longer than 2s
        let (_, duration) = p.exp_regex("[0-9. ]+ ms")?;
        println!("Roundtrip time: {}", duration);
    }
    p.send_control('c')?;
    Ok(())
}

fn main() {
    do_bash().unwrap_or_else(|e| panic!("bash job failed with {}", e));
}

Example with bash and job control

One frequent bitfall with sending ctrl-c and friends is that you need to somehow ensure that the program has fully loaded, otherwise the ctrl-* goes into nirvana. There are two functions to ensure that:

  • execute where you need to provide a match string which is present on stdout/stderr when the program is ready
  • wait_for_prompt which waits until the prompt is shown again
use rexpect::spawn_bash;
use rexpect::error::*;

fn do_bash_jobcontrol() -> Result<(), Error> {
    let mut p = spawn_bash(Some(1000))?;
    p.execute("ping 8.8.8.8", "bytes of data")?;
    p.send_control('z')?;
    p.wait_for_prompt()?;
    // bash writes 'ping 8.8.8.8' to stdout again to state which job was put into background
    p.execute("bg", "ping 8.8.8.8")?;
    p.wait_for_prompt()?;
    p.send_line("sleep 0.5")?;
    p.wait_for_prompt()?;
    // bash writes 'ping 8.8.8.8' to stdout again to state which job was put into foreground
    p.execute("fg", "ping 8.8.8.8")?;
    p.send_control('c')?;
    p.exp_string("packet loss")?;
    Ok(())
}

fn main() {
    do_bash_jobcontrol().unwrap_or_else(|e| panic!("bash with job control failed with {}", e));
}

License

Licensed under either of

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.