From ebba3951aa13d2668bc684680f557b8cbbda8b20 Mon Sep 17 00:00:00 2001
From: Harishankar <v.harishankar@gmail.com>
Date: Sat, 30 May 2020 15:04:23 +0530
Subject: [PATCH] Added command line argument option to run as a single command
 Added command line option to run the program as a single command instead of
 interactive mode

---
 src/main.rs | 94 +++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 66 insertions(+), 28 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index bab1e52..2154ba5 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -3,6 +3,7 @@ use std::io::Write;
 use regex::Regex;
 use ansi_term::Colour;
 use ansi_term::Style;
+use std::env;
 
 const ILLEGAL_EXP : &'static str = "Illegal Expression";
 const ERR_PARSING_NOT_MATCH : &'static str = "Error parsing expression! \
@@ -134,38 +135,26 @@ fn evaluate (expr : &str, match_num : &regex::Regex) -> Result<f32,String> {
 }
 
 fn main() {
-	// get a line from input and evaluate it 
-	let mut expr = String::new ();
+
+	let args : Vec<String> = env::args().collect ();
 	// regular expression to match a number 
 	let match_num = Regex::new (r"^\d+?\.*?\d*?$").unwrap ();
-	// loop until a blank line is received	
-	loop {
-		expr.clear ();	
-		print!("{}", Style::new().bold().paint("evpf>"));
-		io::stdout().flush ().expect (ERR_FLUSHING);
-		// read a line of text
-		io::stdin().read_line (&mut expr).expect (ERR_READING_LINE);
-		// trim the text
-		let expr = expr.trim ();
-
-		if expr == "q" || expr == "Q" {
-		// quit if the expression is q or Qs 
-			break;
-		} else if expr == "?" || expr == "h" || expr == "H" {
-		// display help text
-			for text in HELP_TEXT.iter() {
-				println! ("{}", Colour::Cyan.paint(*text));
+	
+	if args.len () > 1 {
+	// if arguments are provided run in command line mode - i.e. print the 
+	// result and exit	
+		let mut expr = String::new ();
+		let mut i = 0;
+		// create the expression string to evaluate
+		for arg in args.iter() {
+			if i > 0 {
+				expr.push_str (&arg);
+				expr.push_str (" ");
 			}
-
-			continue;
-		} else if expr == "" {
-		// continue without proceeding
-			continue;
+			i += 1;
 		}
-		
-		// Evaluate result
+		// evaluate the result 
 		let res = evaluate (&expr, &match_num);
-		
 		// if Result is OK then print the result in green
 		if res.is_ok () {
 			let restxt = format! ("{}: {}", RESULT, 
@@ -176,7 +165,56 @@ fn main() {
 			let errtxt = format! ("{}: {}", ERROR, 
 											res.unwrap_err());
 			eprintln! ("{}", Colour::Purple.paint (errtxt));
-			eprintln! ("{}", Colour::Purple.paint (ERROR_HELP));
+		}		
+		
+	} else {
+		// if arguments are not provided run in interactive mode - 
+		// display a prompt and get the expression 
+		// repeat until the user quits
+		
+		// get a line from input and evaluate it 
+		let mut expr = String::new ();
+
+		// loop until a blank line is received	
+		loop {
+			expr.clear ();	
+			print!("{}", Style::new().bold().paint("evpf>"));
+			io::stdout().flush ().expect (ERR_FLUSHING);
+			// read a line of text
+			io::stdin().read_line (&mut expr).expect (ERR_READING_LINE);
+			// trim the text
+			let expr = expr.trim ();
+
+			if expr == "q" || expr == "Q" {
+			// quit if the expression is q or Qs 
+				break;
+			} else if expr == "?" || expr == "h" || expr == "H" {
+			// display help text
+				for text in HELP_TEXT.iter() {
+					println! ("{}", Colour::Cyan.paint(*text));
+				}
+
+				continue;
+			} else if expr == "" {
+			// continue without proceeding
+				continue;
+			}
+			
+			// Evaluate result
+			let res = evaluate (&expr, &match_num);
+			
+			// if Result is OK then print the result in green
+			if res.is_ok () {
+				let restxt = format! ("{}: {}", RESULT, 
+												res.unwrap());
+				println! ("{}", Colour::Green.paint (restxt));
+			} else {
+			// print the error in purple
+				let errtxt = format! ("{}: {}", ERROR, 
+												res.unwrap_err());
+				eprintln! ("{}", Colour::Purple.paint (errtxt));
+				eprintln! ("{}", Colour::Purple.paint (ERROR_HELP));
+			}
 		}
 	}
 }
-- 
2.20.1