cmd_lib 0.8.3

# 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](https://crates.io/crates/cmd_lib).

## Why you need this
If you need to run some external commands in rust, the
[std::process::Command](https://doc.rust-lang.org/std/process/struct.Command.html) 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](https://en.wikipedia.org/wiki/Redirection_(computing)) or
[Piping](https://en.wikipedia.org/wiki/Redirection_(computing)#Piping) is needed, you need to
set up the parent and child IO handles manually, like this in the
[rust cookbook](https://rust-lang-nursery.github.io/rust-cookbook/os/external.html), which is often a tedious
work.

A lot 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. For the [rust cookbook examples](https://rust-lang-nursry.github.io/rust-cookbook/os/external.html),
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](https://github.com/rust-shell-script/rust_cmd_lib/blob/master/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
    ```rust
    use cmd_lib::run_cmd;
    let msg = "I love rust";
    run_cmd!(echo $msg)?;
    run_cmd!(|msg| echo "This is the message: $msg")?;

    // pipe commands are also supported
    run_cmd!(du -ah . | sort -hr | head -n 10)?;

    // 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() {
        eprintln!("Run group command failed");
    }
    ```

- run_fun! --> FunResult
    ```rust
    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](https://doc.rust-lang.org/reference/tokens.html#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.

If they are part of string literals, you need to capture the declarations with `| a, b, ... |` at the macros'
beginnings. e.g.
```rust
let msg = "I love rust";
run_cmd!(echo $msg)?;
run_cmd!(|msg| echo "This is the message: $msg")?;
```
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](https://doc.rust-lang.org/reference/tokens.html#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:
```rust
// 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)?;
```

### Redirection and Piping
Right now piping and stdin, stdout, stderr redirections are supported. Most parts are the same as in
[bash scripts](https://www.gnu.org/software/bash/manual/html_node/Redirections.html#Redirections).
See examples at [examples/redirect.rs](https://github.com/rust-shell-script/rust_cmd_lib/blob/master/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
```rust
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
```

### Macros to set scoped process environment variables
- `proc_env_set!` to define process running related environment variables
- Right now, only `PWD` and `CMD_LIB_DEBUG` are supported
- More variables like GID, UID, UMASK ... are on the way
```rust
use cmd_lib::{proc_env_set, run_cmd, run_fun, CmdResult};
proc_env_set!(CMD_LIB_DEBUG = 1); // to print commands
{
    proc_env_set!(PWD = "/tmp");
    run_cmd!(pwd)?;
}
run_cmd!(pwd)?;
```

### Builtin commands
#### cd
cd: set process current directory
```rust
run_cmd! {
    cd /tmp;
    ls | wc -l;
};
```
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.

## Complete Example
See `examples` directory, which contains a [tetris game](https://github.com/rust-shell-script/rust_cmd_lib/blob/master/examples/tetris.rs)
converted from bash implementation and other simple examples.

## Related

See [rust-shell-script](https://github.com/rust-shell-script/rust-shell-script/), which can compile
rust-shell-script scripting language directly into rust code.