Regular Expression for alphanumeric and underscores

Question

I would like to have a regular expression that checks if a string contains only upper and lowercase letters, numbers, and underscores.

Answer 1

There's a lot of verbosity in here, and I'm deeply against it, so, my conclusive answer would be:

/^\w+$/

\w is equivalent to [A-Za-z0-9_], which is pretty much what you want. (unless we introduce unicode to the mix)

Using the + quantifier you'll match one or more characters. If you want to accept an empty string too, use * instead.

Answer 2

In Computer Science, an Alphanumeric value often means the first character is not a number but is an alphabet or underscore. Thereafter the character can be 0-9, A-Z, a-z, or underscore (_).

Here is how you would do that:

Tested under php:

$regex = '/^[A-Za-z_][A-Za-z\d_]*$/'

or take this

^[A-Za-z_][A-Za-z\d_]*$

and place it in your development language.

Answer 3

Here is the regex for what you want with a quantifier to specify at least 1 character and no more than 255 characters

[^a-zA-Z0-9 _]{1,255}

Answer 4

Required Format Allow these 3:

1. 0142171547295
2. 014-2171547295
3. 123abc

Don't Allow other formats:

validatePnrAndTicketNumber(){
    let alphaNumericRegex=/^[a-zA-Z0-9]*$/;
    let numericRegex=/^[0-9]*$/;
    let numericdashRegex=/^(([1-9]{3})\-?([0-9]{10}))$/;
   this.currBookingRefValue = this.requestForm.controls["bookingReference"].value;
   if(this.currBookingRefValue.length == 14 && this.currBookingRefValue.match(numericdashRegex)){
     this.requestForm.controls["bookingReference"].setErrors({'pattern': false});
   }else if(this.currBookingRefValue.length ==6 && this.currBookingRefValue.match(alphaNumericRegex)){
    this.requestForm.controls["bookingReference"].setErrors({'pattern': false});
   }else if(this.currBookingRefValue.length ==13 && this.currBookingRefValue.match(numericRegex) ){
    this.requestForm.controls["bookingReference"].setErrors({'pattern': false});
   }else{
    this.requestForm.controls["bookingReference"].setErrors({'pattern': true});
   }
}

<input name="booking_reference" type="text" [class.input-not-empty]="bookingRef.value"
    class="glyph-input form-control floating-label-input" id="bookings_bookingReference"
    value="" maxlength="14" aria-required="true" role="textbox" #bookingRef
    formControlName="bookingReference" (focus)="resetMessageField()" (blur)="validatePnrAndTicketNumber()"/>

Answer 5

^\w*$ will work for below combinations

1
123
1av
pRo
av1

Answer 6

For me there was an issue in that I want to distinguish between alpha, numeric and alpha numeric, so to ensure an alphanumeric string contains at least one alpha and at least one numeric, I used :

^([a-zA-Z_]{1,}\d{1,})+|(\d{1,}[a-zA-Z_]{1,})+$