使用正则表达式检测单词后跟点或空格

Question

I am using regex and C# to find occurrences of a particular word using

Regex regex = new Regex(@"\b" + word + @"\b");

How can I modify my Regex to only detect the word if it is either preceded with a whitespace, followed with a whitespace or followed with a dot?

Examples:

this.Button.Value - should match this.value - should match

document.thisButton.Value - should not match

Answer 1

Regex regex = new Regex(@"((?<=( \.))" + word + @"\b)" + "|" + @"(\b" + word + @"[ .])");

However, note that this could cause trouble if word contains characters that have special meanings in Regular Expressions. I'm assuming that word contains alpha-numeric characters only.

Answer 2

如果我正确理解你：

Regex regex = new Regex(@"\b" + (word " " || ".") + @"\b");

Answer 3

You may use lookarounds and alternation to check for the 2 possibilities when a keyword is enclosed with spaces or is just followed with a dot:

var line = "this.Button.Value\nthis.value\ndocument.thisButton.Value";
var word = "this";
var rx =new Regex(string.Format(@"(?<=\s)\b{0}\b(?=\s)|\b{0}\b(?=\.)", word));
var result = rx.Replace(line, "NEW_WORD");
Console.WriteLine(result);

See IDEONE demo and a regex demo .

The pattern matches:

• (?<=\\s)\\bthis\\b(?=\\s) - whole word "this" that is preceded with whitespace (?<=\\s) and that is followed with whitespace (?=\\s)
• | - or
• \\bthis\\b(?=\\.) - whole word "this" that is followed with a literal . ( (?=\\.) )

Since lookarounds are not consuming characters (the regex index remains where it was) the characters matched with them are not placed in the match value, and are thus untouched during the replacement.

Answer 4

The (?<=...) match group checks for preceding and (?=...) checks for following, both without including them in the match.

Regex regex = new Regex(@"(?<=\s)\b" + word + @"\b|\b" + word + @"\b(?=[\s\.])");

EDIT: Pattern updated.

EDIT 2: Online test: http://ideone.com/RXRQM5