php regular expression to check whether a number consists of 5 digits

Question

how to write a regular expression to check whether a number is consisting only of 5 digits?

Answer 1

This regular expression should work nicely:

/^\d{5}$/

This will check if a string consists of only 5 numbers.

• / is the delimiter. It is at the beginning and the end of a regular expression. (User-defined, you can use any character as delimiter).

• ^ is a start of string anchor.

• \d is a shorthand for [0-9], which is a character class matching only digits.

• {5} means repeat the last group or character 5 times.

• $ is the end of string anchor.

• / is the closing delimiter.

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If you want to make sure that the number doesn't start with 0, you can use the following variant:

/^[1-9]\d{4}$/

Where:

• / is the delimiter. It is at the beginning and the end of a regular expression. (User-defined, you can use any character as delimiter).

• ^ is a start of string anchor.

• [1-9] is a character class matching digits ranging from 1 to 9.

• \d is a shorthand for [0-9], which is a character class matching only digits.

• {4} means repeat the last group or character 4 times.

• $ is the end of string anchor.

• / is the closing delimiter.

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Note that using regular expressions for this kind of validation is far from being ideal.