# Constraint for capturing specific entry in text **URL:** \ **Category:** Support\ **Created:** [July 14, 2014, 3:05pm UTC](https://forum.getodk.org/t/constraint-for-capturing-specific-entry-in-text/3407 "2014-07-14T15:05:37Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Paul\_Burland](https://getodk.b-cdn.net/letter_avatar_proxy/v4/letter/p/58956e/32.png) [@Paul\_Burland](https://forum.getodk.org/u/Paul_Burland)\ **Post date:** [July 14, 2014, 3:05pm UTC](https://forum.getodk.org/t/constraint-for-capturing-specific-entry-in-text/3407/1 "2014-07-14T15:05:37Z")
Hi All, I am trying to create a from whereby inspectors are initially required to enter a valid email address. As such I am trying to use a constraint to check that the entry contains the @ character, but not sure how or if this is the best way to do this. Any assistance would be appreciated. Many thanks, Paul ---
**Author:** ![Koassi\_AKAKPO](https://getodk.b-cdn.net/letter_avatar_proxy/v4/letter/k/e19b73/32.png) [@Koassi\_AKAKPO](https://forum.getodk.org/u/Koassi_AKAKPO)\ **Post date:** [July 14, 2014, 6:37pm UTC](https://forum.getodk.org/t/constraint-for-capturing-specific-entry-in-text/3407/2 "2014-07-14T18:37:14Z")
[http://opendatakit.org/help/form-design/binding/](http://opendatakit.org/help/form-design/binding/) Regular Expression: Answer must be an email address like [bob@aol.com](mailto:bob@aol.com) > **···** > > Le lundi 14 juillet 2014 15:05:37 UTC, Paul Burland a écrit : \> \> Hi All, \> \> I am trying to create a from whereby inspectors are initially required to \> enter a valid email address. As such I am trying to use a constraint to \> check that the entry contains the @ character, but not sure how or if this \> is the best way to do this. \> \> Any assistance would be appreciated. \> \> Many thanks, \> Paul \> ---
**Author:** ![Paul\_Burland](https://getodk.b-cdn.net/letter_avatar_proxy/v4/letter/p/58956e/32.png) [@Paul\_Burland](https://forum.getodk.org/u/Paul_Burland)\ **Post date:** [July 15, 2014, 7:40am UTC](https://forum.getodk.org/t/constraint-for-capturing-specific-entry-in-text/3407/3 "2014-07-15T07:40:39Z")
Many thanks, cannot believe I missed that!! Regards, Paul > **···** > > On Monday, 14 July 2014 19:37:15 UTC+1, Mokpokpo ADJEODA wrote: \> \> http://opendatakit.org/help/form-design/binding/ \> Regular Expression: Answer must be an email address like b...@aol.com \> \> \> constraint="regex(., '[A-Za-z0-9.\_%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,4}')" \> jr:constraintMsg="this isn't a valid email address"/\> \> \> Le lundi 14 juillet 2014 15:05:37 UTC, Paul Burland a écrit : \>\> \>\> Hi All, \>\> \>\> I am trying to create a from whereby inspectors are initially required to \>\> enter a valid email address. As such I am trying to use a constraint to \>\> check that the entry contains the @ character, but not sure how or if this \>\> is the best way to do this. \>\> \>\> Any assistance would be appreciated. \>\> \>\> Many thanks, \>\> Paul \>\> \> ---
**Author:** ![MKamal](https://getodk.b-cdn.net/letter_avatar_proxy/v4/letter/m/43a26b/32.png) [@MKamal](https://forum.getodk.org/u/MKamal)\ **Post date:** [June 4, 2018, 12:57pm UTC](https://forum.getodk.org/t/constraint-for-capturing-specific-entry-in-text/3407/4 "2018-06-04T12:57:41Z")
could u help me with the solution as the URL that u r posted is not working. Many thanks. ---
**Author:** ![LN](https://getodk.b-cdn.net/user_avatar/forum.getodk.org/ln/32/1605_2.png) [@LN](https://forum.getodk.org/u/LN)\ **Post date:** [June 4, 2018, 9:24pm UTC](https://forum.getodk.org/t/constraint-for-capturing-specific-entry-in-text/3407/5 "2018-06-04T21:24:17Z")
You can read more about using regular expression constraints at [https://docs.opendatakit.org/form-regex/](https://docs.opendatakit.org/form-regex/). In particular, the page at [https://gist.github.com/nerdsrescueme/1237767](https://gist.github.com/nerdsrescueme/1237767) has several examples you will be interested in. The website was recently updated and some redirects may not be as helpful as they can be. @adammichaelwood I'm wondering whether [http://opendatakit.org/help/form-design/binding/](http://opendatakit.org/help/form-design/binding/) should perhaps redirect to [https://docs.opendatakit.org/form-logic](https://docs.opendatakit.org/form-logic)? It would also be helpful to have some examples that used to be on that page shown inline. ---
**Author:** ![Xiphware](https://getodk.b-cdn.net/user_avatar/forum.getodk.org/xiphware/32/2587_2.png) [@Xiphware](https://forum.getodk.org/u/Xiphware)\ **Post date:** [June 4, 2018, 9:31pm UTC](https://forum.getodk.org/t/constraint-for-capturing-specific-entry-in-text/3407/6 "2018-06-04T21:31:10Z")
As others have indicated, what you are looking for is to use a [regular expression](https://docs.opendatakit.org/form-regex/); ie `constraint='regex(...)'` Of course, the real issue is what is the proper regex for checking an email address? Well... that all rather depends on how precise you wanna get! If you want to be **really** pedantic about it, there's this: `(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'\*+/=?^\_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])` (and no, I didnt come up with that myself 🙂 ) Check out [email regex](http://emailregex.com/) if you want all the gory details. Basically, you will have to make a decision how precise you want your check to be - you can _really_ go nuts trying to come up with a regex that'll accept 100% valid emails and reject 100% invalid ones... ---
**Author:** ![adammichaelwood](https://getodk.b-cdn.net/user_avatar/forum.getodk.org/adammichaelwood/32/1698_2.png) [@adammichaelwood](https://forum.getodk.org/u/adammichaelwood)\ **Post date:** [June 12, 2018, 3:26pm UTC](https://forum.getodk.org/t/constraint-for-capturing-specific-entry-in-text/3407/7 "2018-06-12T15:26:38Z")
Depending on your context, you need to be aware of issues with expanded Unicode support in email. cf: [https://en.wikipedia.org/wiki/International\_email](https://en.wikipedia.org/wiki/International_email) [Valid](https://tools.ietf.org/html/rfc6530) email addresses that fail the regex above: 用户@例子.广告 अजय@डाटा.भारत квіточка@пошта.укр θσερ@εχαμπλε.ψομ Dörte@Sörensen.example.co аджай@экзампл.рус وأشوكا @ الهند