正则表达式替换用短划线包围的一个字母

Question

I try to replace a specific letter surrounded by one or two dashes with another letter

Examples : modif-i-ed => modifyed (-i- is replaced with y)

a-im => eim (a- is replaced with e)

I tried

Regex.Replace(word, "-?([a-zA-Z])-", new_letter)

But it generates for example modiyyed for the first example.

Answer 1

The problem is that once the first - becomes optional, there are 2 matches inside modif-i-ed : f- and i- . Thus, there are two replacements.

I suggest matching and capturing the letters before the -X- pattern and then return them as is in the Match evaluator, and use -?[az]- to match and then replace:

(\B[a-z](?=-))|-?[a-z]-

C#:

var myLetter = "y";
var str = " modif-i-ed  a-im  y-i-eld";
var res = Regex.Replace(str, @"(\B[a-z](?=-))|-?[a-z]-",
      m => m.Groups[1].Success ? m.Groups[1].Value : myLetter);
Console.WriteLine(res); // => modifyed  yim  yyeld

See IDEONE demo