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# Regex for one digit number

A digit is a numerical symbol used in mathematical notation to represent a number. In the decimal number system, which is the most common number system used in the world today, there are ten digits: 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. These digits are used to represent all possible numbers, including integers (whole numbers), fractions, and decimals. 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 a digit/number

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.

# Regex for checking if one digit/number is valid or not

Regular Expression for digit/number-

```
/^\d$/gm
```

Test string examples for the above regex-

Input String | Match Output |
---|---|

ae | does not match |

12 | does not match |

2 | matches |

7 | matches |

4 | matches |

Here is a detailed explanation of the above regex-

```
/^\d$/gm
^ asserts position at start of a line
\d matches a digit (equivalent to [0-9])
$ asserts position at the end of a line
Global pattern flags
m modifier: multi line. Causes ^ and $ to match the begin/end of each line (not only begin/end of string)
g modifier: global. All matches (don't return after first match)
```

Hope this article was useful to check if the string is a valid single digit/number or not.