#shell #scripts #commandline #subprocess #pipeline

cmd_lib

Common rust commandline macros and utils, to write shell script like tasks easily

52 releases

new 0.10.5 Mar 1, 2021
0.10.2 Feb 25, 2021
0.8.5 Oct 17, 2020
0.8.2 Jul 21, 2020
0.7.8 Oct 2, 2019

#23 in Rust patterns

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Used in 10 crates (7 directly)

MIT/Apache

36KB
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cmd_lib

Rust command-line library

Common rust command-line macros and utilities, to write shell-script like tasks easily in rust programming language. Available at crates.io.

Why you need this

If you need to run some external commands in rust, the std::process::Command is a good abstraction layer on top of different OS syscalls. It provides fine-grained control over how a new process should be spawned, and it allows you to wait for process to finish and check the exit status or collect all of its output. However, when Redirection or Piping is needed, you need to set up the parent and child IO handles manually, like this in the rust cookbook, which is often a tedious work.

A lot of developers just choose shell(sh, bash, ...) scripts for such tasks, by using < to redirect input, > to redirect output and '|' to pipe outputs. In my experience, this is the only good parts of shell script. You can find all kinds of pitfalls and mysterious tricks to make other parts of shell script work. As the shell scripts grow, they will ultimately be unmaintainable and no one wants to touch them any more.

This cmd_lib library is trying to provide the redirection and piping capabilities, and other facilities to make writing shell-script like tasks easily without launching any shell. For the rust cookbook examples, they can usually be implemented as one line of rust macro with the help of this library, as in the examples/rust_cookbook_external.rs. Since they are rust code, you can always rewrite them in rust natively in the future, if necessary without spawning external commands.

What this library provides

Macros to run external commands

  • run_cmd! --> CmdResult

    use cmd_lib::run_cmd;
    let msg = "I love rust";
    run_cmd!(echo $msg).unwrap();
    run_cmd!(echo "This is the message: $msg").unwrap();
    
    // pipe commands are also supported
    run_cmd!(du -ah . | sort -hr | head -n 10).unwrap();
    
    // or a group of commands
    // if any command fails, just return Err(...)
    let file = "/tmp/f";
    let keyword = "rust";
    if run_cmd! {
        cat ${file} | grep ${keyword};
        echo "bad cmd" >&2;
        ls /nofile || true;
        date;
        ls oops;
        cat oops;
    }.is_err() {
        // your error handling code
    }
    
  • run_fun! --> FunResult

    use cmd_lib::run_fun;
    let version = run_fun!(rustc --version).unwrap();
    eprintln!("Your rust version is {}", version);
    
    // with pipes
    let n = run_fun!(echo "the quick brown fox jumped over the lazy dog" | wc -w).unwrap();
    eprintln!("There are {} words in above sentence", n);
    

Intuitive parameters passing

When passing parameters to run_cmd! and run_fun! macros, if they are not part to rust String literals, they will be converted to string as an atomic component, so you don't need to quote them. The parameters will be like $a or ${a} in run_cmd! or run_fun! macros.

use cmd_lib::run_cmd;
let dir = "my folder";
run_cmd!(echo "Creating $dir at /tmp").unwrap();
run_cmd!(mkdir -p /tmp/$dir).unwrap();

// or with group commands:
let dir = "my folder";
run_cmd!(echo "Creating $dir at /tmp"; mkdir -p /tmp/$dir).unwrap();

You can consider "" as glue, so everything inside the quotes will be treated as a single atomic component.

If they are part of Raw string literals, there will be no string interpolation, the same as in idiomatic rust. However, you can always use format! macro to form the new string. For example:

use cmd_lib::run_cmd;
// string interpolation
let key_word = "time";
let awk_opts = format!(r#"/{}/ {{print $(NF-3) " " $(NF-1) " " $NF}}"#, key_word);
run_cmd!(ping -c 10 www.google.com | awk $awk_opts).unwrap();

If you want to use dynamic parameters, you can use $[] to access vector variable:

use cmd_lib::run_cmd;
let gopts = vec![vec!["-l", "-a", "/"], vec!["-a", "/var"]];
for opts in gopts {
    run_cmd!(ls $[opts]).unwrap();
}

Redirection and Piping

Right now piping and stdin, stdout, stderr redirection are supported. Most parts are the same as in bash scripts. See examples at examples/redirect.rs

Macros to define, get and set global variables

  • proc_var! to define thread local global variable
  • proc_var_get! to get the value
  • proc_var_set! to set the value
use cmd_lib::{ proc_var, proc_var_get, proc_var_set };
proc_var!(DELAY, f64, 1.0);
const DELAY_FACTOR: f64 = 0.8;
proc_var_set!(DELAY, |d| *d *= DELAY_FACTOR);
let d = proc_var_get!(DELAY);
// check more examples in examples/tetris.rs

Builtin commands

cd

cd: set process current directory

use cmd_lib::run_cmd;
run_cmd! (
    cd /tmp;
    ls | wc -l;
).unwrap();

Notice that builtin cd will only change with current scope and it will restore the previous current directory when it exits the scope.

Use std::env::set_current_dir if you want to change the current working directory for the whole program.

Macros to register your own commands

Declare your function with export_cmd attribute:

use cmd_lib::{export_cmd, use_cmd, run_cmd, run_fun, CmdArgs, CmdEnvs, FunResult};
#[export_cmd(my_cmd)]
fn foo(args: CmdArgs, _envs: CmdEnvs) -> FunResult {
    println!("msg from foo(), args: {:?}", args);
    Ok("bar".into())
}

// To use it, just import it at first:
use_cmd!(my_cmd);
run_cmd!(my_cmd).unwrap();
println!("get result: {}", run_fun!(my_cmd).unwrap());

See examples in examples/test_export_cmds.rs

Other Notes

Environment Variables

You can use std::env::var to fetch the environment variable key from the current process. It will report error if the environment variable is not present, and it also includes other checks to avoid silent failures.

To set environment variables for the command only, you can put the assignments before the command. Like this:

use cmd_lib::run_cmd;
run_cmd!(FOO=100 /tmp/test_run_cmd_lib.sh).unwrap();

Security Notes

Using macros can actually avoid command injection, since we do parsing before variable substitution. For example, below code is fine even without any quotes:

use cmd_lib::{run_cmd, CmdResult};
fn cleanup_uploaded_file(file: &str) -> CmdResult {
    run_cmd!(/bin/rm -f /var/upload/$file)
}

It is not the case in bash, which will always do variable substitution at first.

Glob/Wildcard

This library does not provide glob functions, to avoid silent errors and other surprises. You can use the glob package instead.

Thread Safety

This library tries very hard to not set global states, so parallel cargo test can be executed just fine. However, the process APIs are inherently not thread-safe, as a result I sometimes need to set RUST_TEST_THREADS=1 before running tests.

License: MIT OR Apache-2.0

Dependencies

~0.4–0.8MB
~20K SLoC