Replace only leading and trailing whitespace with underscore using regex in c#

Question

I want to replace only leading and trailing white space of a string by number of underscore.

Input String

" New Folder  "

(Notes: There is one white space at front and two white spaces at the end of this string)

Output

My desire output string "_New Folder__"
(The output string has one underscore at the front and two underscore at the end.)

Kobi · Accepted Answer · 2010-12-28 11:00:00Z

4

One solution is using a callback:

s = Regex.Replace(s, @"^\s+|\s+$", match => match.Value.Replace(' ', '_'));

Or using lookaround (a bit trickier):

s = Regex.Replace(s, @"(?<=^\s*)\s|\s(?=\s*$)", "_");

answered Dec 28, 2010 at 11:00

Kobi

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2 Comments

Kobi Over a year ago

Looking again, new String('_', match.Length) might be more appropriate here. Oh well.

Brian Over a year ago

Definitely. Not only is it more obvious what is being done, but it also has the benefit of handling other whitespace characters besides space.

Kobi · Accepted Answer · 2010-12-28 11:07:35Z

1

You may also choose a non-regex solution, but I'm not sure it's pretty:

StringBuilder sb = new StringBuilder(s);
int length = sb.Length;
for (int postion = 0; (postion < length) && (sb[postion] == ' '); postion++)
    sb[postion] = '_';
for (int postion = length - 1; (postion > 0) && (sb[postion] == ' '); postion--)
    sb[postion] = '_';
s = sb.ToString();

answered Dec 28, 2010 at 11:07

Kobi

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1 Comment

Kobi Over a year ago

I think I've answered too many regular expression questions, I'm sure there's a better way to do this :P

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