问题描述:

I want to pad left every number with zeroes (it has to be 8 digits) in my string.

e.g.

`asd 123 rete > asd 00000123 rete`

4444 my text > 00004444 my text

Is it possible to do this using regular expressions? Especially `Regex.Replace()`

?

Notice that the number of zeroes is different for different numbers. I mean the padded number has to be 8 digits long.

Microsoft has built in functions for this:

```
someString = someString.PadLeft(8, '0');
```

And here's an article on MSDN

To use a regular expression, do something like this:

```
string someText = "asd 123 rete";
someText = Regex.Replace(someText, @"\d+", n => n.Value.PadLeft(8, '0'));
```

Thread is old but maybe someone needs this.

Nickon states he wants to use regex. Why? Doesn't matter, maybe its fun. I had to do a inline replace in SQL so some home made SQL functions that calls a C# regex has been helpful.

What I needed to pad looked something like this:

```
abc 1.1.1
abc 1.2.1
abc 1.10.1
```

and I wanted:

```
abc 001.001.001
abc 001.002.001
abc 001.010.001
```

So I could sort it alphabetiacally.

The only solution so far (that I found) was to do the padding and truncating to right length in two steps. I couldn't use a Lambda since this was in SQL and I hadn't prepared my functions for that.

```
//This pads any numbers and truncates it to a length of 8
var unpaddedData = "...";
var paddedData = Regex.Replace(unpaddedData , "(?<=[^\d])(?<digits>\d+)",
"0000000${digits}");
var zeroPaddedDataOfRightLength = Regex.Replace(paddedData ,"\d+(?=\d{8})","");
```

Explanations:

```
(?<=[^\d])(?<digits>\d+)
(?<=[^\d]) Look behind for any non digit, this is needed if there are
more groups of numbers that needs to be padded
(?<digits>\d+) Find the numbers and put them in a group named digits to be
used in the replacement pattern
0000000${digits} Pads all the digits matches with 7 zeros
\d+(?=\d{8}) Finds all digits that are followed by at exactly 8 digits.
?= Doesn't capture the 8 digits.
Regex.Replace(...,"\d+(?=\d{8})","")
Replaces the leading digits with nothing leaving the last 8.
```

If you don't have any attachment to Regex just use format strings:

C# convert int to string with padding zeros?

http://www.xtremedotnettalk.com/showthread.php?t=101461