I'm trying to create a simple command line date entry function.
I get a weird behavior when using regexp pattern matching with golang: correct pattern mach returns false but messes with my loop while incorrect pattern just returns false. Here is the function that produces the error:
func ReadDate(fieldname string) (value string) {
var validID = regexp.MustCompile(`^\d\d\d\d\s(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dez)\s\d\d$`)
for {
value = ""
fmt.Printf("%s - e.g. 2014 Jan 01: ", fieldname)
fmt.Scanf("%s
", &value)
if value == "" {
break // empty value is ok for input
}
fmt.Printf("validid %v
", validID.MatchString(value))
if validID.MatchString(value) {
break
} else {
fmt.Printf("invalid entry, try again..
")
}
}
return
}
when I run it, I get the following:
date - e.g. 2014 Jan 01: x
validid false
date - e.g. 2014 Jan 01: x
validid false
date - e.g. 2014 Jan 01: 2014 Jan 01
validid false
date - e.g. 2014 Jan 01: validid false
date - e.g. 2014 Jan 01: validid false
date - e.g. 2014 Jan 01:
Notice how the last entry with the correct pattern runs another two times through the infinite loop and then stops. Any ideas why this might happen?
Go version 1.2 Linux/386
the problem is Scanf returns before the whole line is read. I've modified your code to use bufio.Scanner and os.Stdin, and it works now:
package main
import (
"bufio"
"fmt"
"os"
"regexp"
)
func ReadDate(fieldname string) (value string) {
var validID = regexp.MustCompile(`^\d\d\d\d\s(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dez)\s\d\d$`)
fmt.Printf("%s - e.g. 2014 Jan 01: ", fieldname)
scanner := bufio.NewScanner(os.Stdin)
for scanner.Scan() {
value = scanner.Text()
fmt.Printf("Read value: '%s'
", value)
if value == "" {
break // empty value is ok for input
}
fmt.Printf("validid %v
", validID.MatchString(value))
if validID.MatchString(value) {
break
} else {
fmt.Printf("invalid entry, try again..
")
}
fmt.Printf("%s - e.g. 2014 Jan 01: ", fieldname)
}
return
}
func main() {
fmt.Println("Returned ", ReadDate("foo"))
}