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Powerful Command-Line Applications in Go

Final Touches to the Initial Version of colStats

Explore the process of finalizing the initial version of the colStats command-line tool in Go. Understand how to create the main.go file, define main and run functions, validate user inputs, process CSV files, and output results using interfaces. This lesson prepares you to implement a functional, user-friendly CLI application and sets the stage for testing and improving its performance.

We'll cover the following...

Creating the main.go file

We create the file main.go to define the main() function. We open the file and add the package and import sections.

We’ll need the following packages:

  • flag: To parse command-line options.
  • fmt: To print formatted output and create new errors.
  • io: So we can use the io.Writer interface.
  • os: To interact with the operating system.

Go (1.6.2)
package main
import (
  "flag"
  "fmt"
  "io"
  "os"
)
Adding the package and import section

Creating the main() function

Next, we create the function main() to parse the command-line arguments and call the function run(), which is responsible for the main logic of the tool.

Go (1.6.2)
func main() {
  // Verify and parse arguments
  op := flag.String("op", "sum", "Operation to be executed")
  column := flag.Int("col", 1, "CSV column on which to execute operation")
  flag.Parse()
  if err := run(flag.Args(), *op, *column, os.Stdout); err != nil {
    fmt.Fprintln(os.Stderr, err)
    os.Exit(1)
  }
}
Adding the package and import section

If the run() function returns any errors, we print them out to ...