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I need to match (using regex) strings that can be like this:

required: custodian_{number 1 - 9}_{fieldType either txt or ssn} optional: _{fieldLength 1-999}

So for example: custodian_1_ssn_1 is valid custodian_1_ssn_1_255 is valid

custodian or custodian_ or custodian_1 or custodian_1_ or custodian_1_ssn or custodian_1_ssn_ or custodian_1_ssn_1_ are not valid

Currently I am working with this:

(?:custodian|signer)_[1-9]?[0-9]_(?:txt|ssn)_[1-9][0-9]?(_[1-9]?[0-9]?[0-9]?)?

as my regex and my api is working to pick up: custodian_1_txt_1 custodian_1_ssn_1 custodian_1_txt_1_255 <---- not matching the last "5"

any thoughts?

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  • 1
    IMHO you shouldn't be using Regex for this. It would probably be easier and faster to use something like string.Split('_') and then iterate over the resulting array, checking for validity and required attributes. Commented Aug 8, 2018 at 17:25
  • 2
    Your best bet is to play with it in a RegEx tool: regex101.com/r/s9ilVe/1 Commented Aug 8, 2018 at 17:28
  • You say you want to match numbers 1-9 for the first field, but [1-9]?[0-9] would match 0-99. Why is the first digit optional, and why is there a second digit at all? Commented Aug 8, 2018 at 17:34

4 Answers 4

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You may use pattern:

^custodian(?:_[a-z0-9]+)+$
  • ^ Assert position beginning of line.
  • custodian Match literal substring custodian.
  • (?:_[a-z0-9]+)+ Non capturing group. Multiple sequence of _ followed by alphanumerics.
  • $ Assert position end of line.

You can check the correct matches here.

Obviously you can modify the pattern to add substring signer in non capturing group as:

^(?:custodian|signer)(?:_[a-z0-9]+)+$.

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1 Comment

I chose this as the answer because it works in all cases I tried. Although, it seems it would works for something out of scope as well IE: custodian_1_xxx_1_15 where xxx is not an acceptable sub-string. It's Ok, though, I will document around this.
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I suggest using \d for numbers not yours and this is my code try it:-

(?:custodian|signer)_[1-9]?[0-9]_(?:txt|ssn)_[1-9][0-9]?(_[1-9]?\d*)?

I just added a \d value to the end of your pattern to match all end digits before another match.

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The end bit matches a string ending in _ (with no number). You can fix that by getting rid of the ? after the last [1-9].
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You could use an anchor to assert the start ^ and the end $ of the string and for the last part make at least the first 1-9 not optional or else it would match and underscore at the end:

^(?:custodian|signer)_[1-9]?[0-9]_(?:txt|ssn)_[1-9][0-9]?(_[1-9][0-9]?[0-9]?)?$

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1

If you're only interested in the last digits, this super generic regex will do:

(?:.+)_(\d+)

If you do need to match the whole string, this worked:

^(?:custodian|signer)_\d+_(?:txt|ssn)(?:_\d+)?_(\d+)$
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4 Comments

@UnbearableLightness Well it doesn't match the whole string, but it does match some of it. Added anchors.
Yeah that's better, the last capturing group should be made non capturing though.
@UnbearableLightness OP's regex captures the last group.
Uh, apologies, my bad.

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