In this article let's understand how we can create a regex for digit/number and how regex can be matched for a given digit/number.

Regex (short for regular expression) is a powerful tool used for searching and manipulating text. It is composed of a sequence of digit/numbers that define a search pattern. Regex can be used to find patterns in large amounts of text, validate user input, and manipulate strings. It is widely used in programming languages, text editors, and command line tools.

Structure of digits/numbers

The digit/number should have the following criteria and structure-

• value of a digit should be - 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9.
• it should contain only special characters/numbers.

Regex for checking if only special characters/number is valid or not

Regular Expression for digit/number-

/[^a-z0-9]+$/igm

Test string examples for the above regex-

Note the i modifier in the regex takes care of the UPPERCASE letters.

Here is a detailed explanation of the above regex-

/[^a-z0-9]+$/igm

Match a single character not present in the list below [^a-z0-9]
+ matches the previous token between one and unlimited times, as many times as possible, giving back as needed (greedy)
a-z matches a single character in the range between a (index 97) and z (index 122) (case insensitive)
0-9 matches a single character in the range between 0 (index 48) and 9 (index 57) (case insensitive)
$ asserts position at the end of a line
Global pattern flags
i modifier: insensitive. Case insensitive match (ignores case of [a-zA-Z])
g modifier: global. All matches (don't return after first match)
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)

Hope this article was useful to check if the string is a valid special characters or not.