init (done): everything works as expected

.gitignore

@@ -0,0 +1 @@
+/target

Cargo.toml

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+[package]
+name = "passgen"
+version = "0.1.0"
+authors = ["Sparkenstein <[email protected]>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+rand = "0.7.3"
+clap = "2.33.3"

src/main.rs

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+extern crate clap;
+
+use clap::{App, Arg};
+use rand::{thread_rng, Rng};
+
+fn main() {
+    let mut rng = thread_rng();
+    let matches = App::new("passgen")
+        .version("1.0")
+        .author("@Sparkenstein")
+        .about("Generate Random password on command line")
+        .arg(
+            Arg::with_name("include")
+                .long("include")
+                .short("i")
+                .default_value("nlus")
+                .help("include numbers/upppercase/lowercase/symbols in generated string"),
+        )
+        .arg(
+            Arg::with_name("length")
+                .long("length")
+                .short("l")
+                .takes_value(true)
+                .default_value("16")
+                .help("include lowercase characters in generated string"),
+        )
+        .get_matches();
+    let chars_to_include = matches.value_of("include").unwrap();
+    let mut pass_string = String::from("");
+    if chars_to_include.contains("l") {
+        pass_string += "abcdefghijklmnopqrstuvwxyz";
+    }
+
+    if chars_to_include.contains("n") {
+        pass_string += "0123456789";
+    }
+
+    if chars_to_include.contains("s") {
+        pass_string += ")(*&^%$#@!~";
+    }
+
+    if chars_to_include.contains("u") {
+        pass_string += "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+    }
+
+    let length = matches
+        .value_of("length")
+        .unwrap()
+        .parse::<usize>()
+        .unwrap();
+    let password = (0..length)
+        .map(|_| {
+            let idx = rng.gen_range(0, pass_string.len());
+            pass_string.chars().nth(idx).unwrap()
+        })
+        .collect::<String>();
+    println!("{}", password);
+}