How do I do a case insensitive regular expression in Go?

Now, of course, I could write my regular expression to handle both cases, such as regexp.Compile("[a-zA-Z]"), but my regular expression is constructed from a string given by the user:

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

Where s.Name is the name. Which could be something like 'North by Northwest'. Now, the most apparent solution to me would be to walk through each character of s.Name and write '[nN]' for each letter:

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

But I feel this is a rather non-elegant solution. Speed is not really a concern, but I need to know if there is another way.

Solution 1:

You can set a case-insensitive flag as the first item in the regex.

You do this by adding "(?i)" to the beginning of a regex.

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

For a fixed regex it would look like this.

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

For more information about flags, search the regexp/syntax package documentation (or the syntax documentation) for the term "flags".

Solution 2:

You can add a (?i) at the beginning of the pattern to make it case insensitive.

Reference

Solution 3:

I'm not too familiar with Go, but according to this example: http://play.golang.org/p/WgpNhwWWuW

You need to prefix your regex statement with (?i)

Solution 4:

Use the i flag. Quoting the tip documentation:

Grouping:

(re)           numbered capturing group
(?P<name>re)   named & numbered capturing group
(?:re)         non-capturing group
(?flags)       set flags within current group; non-capturing
(?flags:re)    set flags during re; non-capturing

Flag syntax is xyz (set) or -xyz (clear) or xy-z (set xy, clear z). The flags are:

i              case-insensitive (default false)
m              multi-line mode: ^ and $ match begin/end line in addition to begin/end text (default false)
s              let . match \n (default false)
U              ungreedy: swap meaning of x* and x*?, x+ and x+?, etc (default false)