How Can I Efficiently Create Case-Insensitive Regular Expressions in Go?

Case-Insensitive Regular Expressions in Go

Consider a scenario where you're constructing a regular expression from user input, as seen in the following code:

reg, err := regexp.Compile(strings.Replace(s.Name, " ", "[ \._-]", -1))

where s.Name is a string like 'North by Northwest'. You might consider iterating over the characters and manually constructing case-insensitive expressions:

for i := 0; i < len(s.Name); i++ {
  if s.Name[i] == " " {
    fmt.Fprintf(str, "%s[ \._-]", str);
  } else {
    fmt.Fprintf(str, "%s[%s%s]&quot;, str, strings.ToLower(s.Name[i]), strings.ToUpper(s.Name[i]))
  }
}

However, there is a more efficient solution.

Using the Case-Insensitive Flag

You can specify a case-insensitive search by adding the flag (?i) to the beginning of your regex:

reg, err := regexp.Compile("(?i)"+strings.Replace(s.Name, " ", "[ \._-]", -1))

For a fixed regex, this flag can be used as follows:

r := regexp.MustCompile(`(?i)CaSe`)

More information on regex flags can be found in the regexp/syntax package documentation.

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