Regular Expressions Numbers and Letters

What to write a regular expression that validates that the input must be a combination of numbers and letters

Regular expression body:

[0-9]+[a-zA-Z]+[0-9a-zA-Z]*|[a-zA-Z]+[0-9]+[0-9a-zA-Z]*

Explanation: against the following figure, there are two cases:

① At least one number at the beginning, followed by at least one letter, followed by either numbers or letters.

② At least one letter starts, followed by at least one number, followed by either numbers or letters.

Supplementary note: Although some environments use forms such as \d or [:digit:] to represent numbers, or other specific forms corresponding to a specific character set, but this is not universal; therefore, it is recommended to use a common way to write regular expressions, such as [0-9] for numbers, [a-zA-Z] for upper- and lower-case letters, and so on. Of course, for specific programming languages there may be escape characters involved, so please take note of that then.

Image explanation:

How do I write a regular expression that can only enter combinations of numbers and letters?

varp=/(?! ^\d+$)(?! ^[a-zA-Z]+$)[0-9a-zA-Z]{4,23}/

(?! ^\d+$) exclude all numbers

(?! ^[a-zA-Z]+$) excludes all-alphabetic

[0-9a-zA-Z]{4,23} Characters or letters with 4-23 digits, disregarding all-numeric and all-character cases.

if(/^[a-zA-Z0-9]{4,23}$/.test(password)){

alert(‘ok’);

}

Regular expressions with at least one numeric letter:

/^(? =. *[A-Za-z])(? =. *\d)[A-Za-z\d]{4,23}$/

1, String consisting of numbers, 26 letters of the alphabet, or underscores:

^[0-9a-zA-Z_]{1,}$

2, Non-negative integer (positive integer + 0):

^/d+$

3, Positive integer:^[0-9 ][1-9][0-9]

4. Non-positive integer (negative integer + 0): ((-/d+)|(0+))4. Non-positive integer (negative integer + 0): ((-/d+)|(0+))

5. Negative integer:^-[0-9][1-9][0-9]

6. Integer:-? /d+6. integer:-? /d+

7. Non-negative floating-point number (positive floating-point number +0):^/d+(/. /d+)? $

8, positive floating-point number:^(([0-9]+/. [0-9][1-9][0-9])|([0-9][1-9][0-9]/. [0-9]+)|([0-9][1-9][0-9]))

9. Non-positive floating-point number (negative floating-point number +0):((-/d+(/. /d+)?) |(0+(/.0+)?))) 9. Non-positive floating-point number (negative floating-point number + 0):((-/d+(/. /d+)?) |(0+(/.0+)?)) /d+)?) |(0+(/.0+)?)))

10, Negative Floating Point:

^(-(([0-9]+/. [0-9][1-9][0-9])|([0-9][1-9][0-9]/. [0-9]+)|([0-9][1-9][0-9]))

11. String consisting of 26 letters of the alphabet:

^[A-Za-z]+13. String consisting of 26 letters of the alphabet in uppercase:[A-Z]+

12. String consisting of 26 English letters in lower case:

13. String consisting of 26 English letters in lower case:

^[a-z]+15. String consisting of numbers and 26 English letters:[A-Za-z0 -9]+

14. String consisting of numbers and 26 letters of the alphabet: [A-Za-z0-9]+

15. String consisting of numbers, 26 letters of the alphabet, or underscores:

< p>^/w+17. email address: [/w-]+(/. [/w-]+)∗[/w-]+(/. [/w-]+)+

Extended information:

alert() method: warning message box;

The alert method takes one argument, the text string you wish to display to the user.

The string is not in HTML format, the message box provides an “OK” button for the user to close the message box, and the message box is a modal dialog box, meaning that the user must close the message box before proceeding.

For example:

window.alert(“Welcome! Please press OK to continue.”) ;

alert function parameters

str – text to be displayed in the message dialog

alert function says

alert message dialog is usually used for some messages to the user, for example, when incorrect data has been entered in the form.

Tip:The message dialog is provided by the system, so the style font may be different in different browsers.

Tip:The message dialog is exclusive, meaning that the user cannot do anything else until he or she clicks a button in the dialog.

Hint: Message dialogs can often be used for debugging programs.

Examples:

alert(“Hellodream!”);

alert(‘Welcometo&lt;br/&gt;dream!’);

alert(‘Welcometo\ndream!’);

Note the second and third examples above, only the third example enables line breaks, refer to the ASCII code table, line breaks are not possible using the br tag in HTML.

Regular expressions for lowercase letters or numbers

You mean:

If that’s what you mean, then it’s straightforward to write

/^[a-zA-Z\d]+$

Where:

^: indicates the beginning of the string

[a-zA-Z\d]+: is divided into parts:

a-z: denotes any of the lowercase letters a through z

A-Z: denotes any of the uppercase letters A through Z

\d: denotes any of the digits

[xxx]: denotes the characters within the set of xxx

Where xxx, that is, as written above:

a-zA-Z\d

So, the total meaning of [a-zA-Z\d]+ is:

Lowercase letters a to zCapital letters A to ZOne or more of the numbers

$: indicates the end of the string

Related to this, interested in it, you can refer to:

[Tutorial] Detailed explanation of Python regular expressions: []bracket brackets Match a set of characters

[Tutorial] Python regular expression: ‘^’Caret off character/insertion character to match the beginning of the string

[Tutorial] Python regular expression: ‘$’dollar dollar sign to match the end of the string

This is a relatively complex regular expression. Interested can refer to:

[Tutorial] Python re module as an example, hand in hand to teach you, how to start from scratch, write a relatively complex regular expression

Note; Although it is written in python, but the principle of internal, for other languages, such as java, javascript, php, perl, etc., are also common.

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Regular expressions: regular expressions for upper and lower case letters and numbers

1./. \{8,\}/. Match uppercase letters, lowercase letters, Arabic numerals, English punctuation in any of the four symbols \{8,\}Match more than 8 times can also be customized English punctuation /([a-zA-Z0-9]|[custom English symbols])\{8,\}/[a-zA-Z0-9] Match uppercase letters, lowercase letters, Arabic numerals. If this is what it means,then it is written directly as.

2./^[a-zA-Z\d]+$/

it will be fine, where:

^: indicates the beginning of the string

[a-zA-Z\d]+: is divided into several parts:

a-z: indicates that any of the lowercase letters a to z

A-Z: indicates that any of the uppercase letters A to Z

A-Z: indicates that the uppercase letters A to Z

\d:

A-Z: indicates that the uppercase letters A to Z

A-Z: indicates that the uppercase letters A to Z

A-Z: indicates that any of the upper case letters A to Z

\d: denotes any number

[xxx]: denotes a character in the set xxx