Regular expression question

[Lee Kuhn]

I am trying the create a regular expression that will essentially match
characters in the middle of a fixed-length string. The string may be any
characters, but will always be the same length. In other words, as the
regular expression (....)($) matches the "4567" in the string "1234567", how
would I create a similar regular expression that only matches the "45" in
the same string. The same regular expression would match "32" in the string
"00032999".

Any help is greatly appreciated.

 

[Bruno Jouhier [MVP]]

Did you try (..)..$

Bruno.

 

[mikeb]

I am trying the create a regular expression that will essentially match
characters in the middle of a fixed-length string. The string may be any
characters, but will always be the same length. In other words, as the
regular expression (....)($) matches the "4567" in the string "1234567", how
would I create a similar regular expression that only matches the "45" in
the same string. The same regular expression would match "32" in the string
"00032999".

Maybe I'm misunderstanding something, but it seems String.Substring()
would be the thing to use for this.

Using a regex seems like overkill.

 

[Bruno Jouhier [MVP]]

I was wrong, you need curly braces instead of parentheses: {..}..$
But substring should do the job. Why use regexp?

Bruno

 

[Lee Kuhn]

The parentheses seem to work better than the curly braces. However, when I
use (..)..$, I end up with two groups: one is "4567" and the other is "45".
The "match" is still "4567". I need the match to be "45". The reason I am
using a regular expression for this is because I am trying to operate within
the confines of existing code, only modifying the actual regular expression.

Lee

 

[Michael Voss]

Hi!

The parentheses seem to work better than the curly braces. However, when I
use (..)..$, I end up with two groups: one is "4567" and the other is "45".
The "match" is still "4567". I need the match to be "45".

[...snip...]

(?<myGroup>.{2}).{2} would match the "4567" in "1234567", you could find
"45" in Match.Groups["myGroup"].Value

 

[Lee Kuhn]

I can definitely see how I could do what I want with groups (and named
groups). At this point, I am trying to determine if I can use a regular
expression to return a substring from the middle of a number (always the
same length) with Regex.Match.Value. The substring will always be from the
same position within the number.

Any thoughts?

Hi!

The parentheses seem to work better than the curly braces. However, when I
use (..)..$, I end up with two groups: one is "4567" and the other is "45".
The "match" is still "4567". I need the match to be "45".

[...snip...]

(?<myGroup>.{2}).{2} would match the "4567" in "1234567", you could find
"45" in Match.Groups["myGroup"].Value

 

[mikeb]

I can definitely see how I could do what I want with groups (and named
groups). At this point, I am trying to determine if I can use a regular
expression to return a substring from the middle of a number (always the
same length) with Regex.Match.Value. The substring will always be from the
same position within the number.1

Again, why not just use String.Substring()?

Any thoughts?

Hi!

The parentheses seem to work better than the curly braces. However, when

I

use (..)..$, I end up with two groups: one is "4567" and the other is
"45".

The "match" is still "4567". I need the match to be "45".

[...snip...]

(?<myGroup>.{2}).{2} would match the "4567" in "1234567", you could find
"45" in Match.Groups["myGroup"].Value

 

[Lee Kuhn]

Because the code is already written and deployed. The regular expression is
exposed to me as an option.

I can definitely see how I could do what I want with groups (and named
groups). At this point, I am trying to determine if I can use a regular
expression to return a substring from the middle of a number (always the
same length) with Regex.Match.Value. The substring will always be from the
same position within the number.1

Again, why not just use String.Substring()?

Any thoughts?

Hi!

:

The parentheses seem to work better than the curly braces. However,

when

I

use (..)..$, I end up with two groups: one is "4567" and the other is

"45".

The "match" is still "4567". I need the match to be "45".

[...snip...]

(?<myGroup>.{2}).{2} would match the "4567" in "1234567", you could find
"45" in Match.Groups["myGroup"].Value

 

[mikeb]

Because the code is already written and deployed. The regular expression is
exposed to me as an option.

I see. Then I think a regular expression such as:

(??<=^.{2}))(.{4})

would do what you want - for the particular case where you want the
substring to start at index 2 and have a length of 4.

Here's a small method that'll build the appropriate regex expression
when passed in the index and length you want:

public static string SubstringRegex( int start, int len) {
return( String.Format("(??<=^.{{{0}}}))(.{{{1}}})",
start, len));
}

Basically, the first part of the regex is a zero-lenth positive
lookbehind assertion wrapped in a non-capturing group. This matches the
characters at the beginning of the string that you want discarded.

The next bit of the regex is a group that captures the number of
characters you want in your substring.

I can definitely see how I could do what I want with groups (and named
groups). At this point, I am trying to determine if I can use a regular
expression to return a substring from the middle of a number (always the
same length) with Regex.Match.Value. The substring will always be from

the

same position within the number.1

Again, why not just use String.Substring()?

Any thoughts?



Hi!

:


The parentheses seem to work better than the curly braces. However,

when

I


use (..)..$, I end up with two groups: one is "4567" and the other is

"45".


The "match" is still "4567". I need the match to be "45".

[...snip...]

(?<myGroup>.{2}).{2} would match the "4567" in "1234567", you could find
"45" in Match.Groups["myGroup"].Value

 

[Lee Kuhn]

Unbelievable...I think that does exactly what I need. I don't how you came
up with that one. Thanks a lot for your help.

Because the code is already written and deployed. The regular expression is
exposed to me as an option.

I see. Then I think a regular expression such as:

(??<=^.{2}))(.{4})

would do what you want - for the particular case where you want the
substring to start at index 2 and have a length of 4.

Here's a small method that'll build the appropriate regex expression
when passed in the index and length you want:

public static string SubstringRegex( int start, int len) {
return( String.Format("(??<=^.{{{0}}}))(.{{{1}}})",
start, len));
}

Basically, the first part of the regex is a zero-lenth positive
lookbehind assertion wrapped in a non-capturing group. This matches the
characters at the beginning of the string that you want discarded.

The next bit of the regex is a group that captures the number of
characters you want in your substring.

Lee Kuhn wrote:

I can definitely see how I could do what I want with groups (and named
groups). At this point, I am trying to determine if I can use a regular
expression to return a substring from the middle of a number (always the
same length) with Regex.Match.Value. The substring will always be from
the

same position within the number.1

Again, why not just use String.Substring()?


Any thoughts?



Hi!

:


The parentheses seem to work better than the curly braces. However,
when

I


use (..)..$, I end up with two groups: one is "4567" and the other is

"45".


The "match" is still "4567". I need the match to be "45".

[...snip...]

(?<myGroup>.{2}).{2} would match the "4567" in "1234567", you could find
"45" in Match.Groups["myGroup"].Value