Update

Author: wilsonmar

challenge.go

@@ -0,0 +1,39 @@
+/* USAGE: go run challenge.go 1st 2nd 3rd 4th
+// Golang program is coded with features commonly needed:
+// * command-line arguments (-help, -verbose)
+// * Logging
+*/
+
+package main 
+  
+import ( 
+    "fmt"
+    "os"
+) 
+  
+func main() { 
+  
+    // The first argument 
+    // is always program name 
+    myProgramName := os.Args[0] 
+  
+    // this will take 4 
+    // command line arguments 
+    cmdArgs := os.Args[4] 
+  
+    // getting the arguments 
+    // with normal indexing 
+    gettingArgs := os.Args[2] 
+  
+    toGetAllArgs := os.Args[1:] 
+  
+    // it will display 
+    // the program name 
+    fmt.Println(myProgramName) 
+      
+    fmt.Println(cmdArgs) 
+      
+    fmt.Println(gettingArgs) 
+      
+    fmt.Println(toGetAllArgs) 
+} 

go-here.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+
+# go-here.sh in https://github.com/wilsonmar/
+# Set variable $GOHOME to this folder as the default folder where custom Go app source code is kept.
+# (by default ~/go)
+
+export GOPATH="$HOME/gmail_acct/golang-samples"
+go env GOPATH

hello-world.go

@@ -0,0 +1,7 @@
+// This is the minimal Go program, to show Go compiler is installed correctly.
+package main
+import( "fmt"; "time")
+var now = time.Now()
+func main() {
+    fmt.Printf("hello, world at %v",now)
+}

rand

@@ -1,3 +1,4 @@
+
 // range to find match of TZ value
 // From https://www.youtube.com/watch?v=rKnDgT73v8s&t=29m
 // One of the first Go programs shown.

range.go

@@ -0,0 +1,79 @@
+// sample.go 
+// USAGE: go run sample.go add -a=42 -b=23
+//        go run sample.go mul -a=25 -b=4
+
+package main
+
+import( "fmt"; "time"; "os"; "errors"; "flag"; "math"; "strings")
+
+var now = time.Now()  // wall clock
+
+func circleArea(radius float32) (float32, error) {
+    if radius < 0 {
+        return 0, errors.New("ERROR: In call of circleArea: radius should be a positive value.")
+    } else {
+        return math.Pi * radius * radius, nil
+    }
+}
+
+func main() {
+    start_time := time.Now()   // monotonic clock
+    args := os.Args[0]
+    f := strings.Fields(args)
+    for _, v := range f {
+       fmt.Println(v)  // TODO: output in one
+    }
+    fmt.Printf("starting at %v \n", now)  // https://golang.org/pkg/time/#Time.Format
+
+       argLength := len(os.Args[1:])
+    if argLength > 0 {
+        for i, a := range os.Args[1:] {
+        	// TODO: Use defer to concatenate string parts?
+            fmt.Printf("Arg %d is %s\n", i+1, a) 
+        }
+    }
+
+    // Adapted from https://golangdocs.com/flag-package-golang
+    // TODO: Add -verbosity
+    addcmd := flag.NewFlagSet("add", flag.ExitOnError)
+    a_add := addcmd.Int("a", 0, "The value of a")
+    b_add := addcmd.Int("b", 0, "The value of b")
+ 
+    mulcmd := flag.NewFlagSet("mul", flag.ExitOnError)
+    a_mul := mulcmd.Int("a", 0, "The value of a")
+    b_mul := mulcmd.Int("b", 0, "The value of b")
+ 
+    switch os.Args[1] {
+    case "add":
+        addcmd.Parse(os.Args[2:])
+        fmt.Println(*a_add + *b_add)
+    case "mul":
+        mulcmd.Parse(os.Args[2:])
+        fmt.Println(*(a_mul) * (*b_mul))
+    default:
+        fmt.Println("expected add or mul command")
+        os.Exit(1)
+    }
+
+    // Known error (-3 radius input):
+    if area2, err := circleArea(-3); err != nil {
+        fmt.Println(err)
+    } else {
+        fmt.Println(area2)
+    }
+
+    t := time.Now()
+    elapsed := t.Sub(start_time)
+    fmt.Printf("Elapsed: %v\n", elapsed)
+    fmt.Printf("Seconds: %f\n", elapsed.Seconds())
+    fmt.Printf("Minutes: %f\n", elapsed.Minutes())
+
+    defer func(msg string) {
+        if r := recover(); r != nil {
+            fmt.Println("recovered")	
+        }
+        fmt.Println(msg)
+    }("Done.")
+
+//    panic("Die!")  // to test defer function to recover
+}

sample.go

@@ -0,0 +1 @@
+sample_test.go

sample_test.go

@@ -22,7 +22,7 @@ import ( // PROTIP: avoid errors with semicolons vs. commas by using a list:
 
 const (
     // For use with http://golang.org/pkg/time/#Parse
-    timeLayout = "2006-01-02 15:04 MST"
+    timeLayout = "2020-01-02 15:04 MST"
 )
 
 // The one of a few reasons for a global variable: