Sscanf not properly matching single quotes

I working on some Go code but I am having troubles figuring out why my string isn't being scanned correctly.

I'm given a string that looks like this:

"ERROR: 1: something happened 'here'"

I'm trying to scan it like this:

n, err := fmt.Sscanf("ERROR: 1: something happened 'here'", "ERROR: 1: something happened '%50s'", &value)

However, every time I check the result of the value, I get something like this:

here'

Where the last single quote is left in.

Any idea how to fix this? I figured this case wouldn't be non-deterministic because the function can't complete formatting without including the quote.

Of course, I can simply remove the last character, but I would prefer a fmt-based solution.

The builtin fmt.Scanner has no way to do what you're trying to do. If the target text was wrapped in double quotes, you could use the %q specifier.

Alternatively, if the target was a single wrapped character, you could use text/scanner. But because your target is neither of those, there's nothing built in. So, your options are regexp, or bufio with a custom scanner, or even just strings.Split. If you insist on using fmt you can do a custom scanner, but it's probably the worst option of everything:

package main
import "fmt"

type quote struct { tok string }

func (q *quote) Scan(state fmt.ScanState, verb rune) error {
   tok, err := state.Token(false, func(r rune) bool {
      return r != 0x27 // '
   })
   if err != nil {
      return err
   }
   if _, _, err := state.ReadRune(); err != nil {
      if len(tok) == 0 {
         panic(err)
      }
   }
   q.tok = string(tok)
   return nil
}

Example:

package main

import (
   "fmt"
   "strings"
)

func main() {
   r := strings.NewReader("ERROR: 1: something happened 'here'")
   for {
      var q quote
      _, err := fmt.Fscan(r, &q)
      if err != nil {
         break
      }
      fmt.Printf("%q\n", q.tok)
   }
}

Result:

"ERROR: 1: something happened "
"here"