How to validate NUMBERS with a regular expression?

 It depends. What type of number? What precision? What length? What do you want as a decimal separator? Etc. The following examples should help you want with the most common tasks.

Positive integers of undefined length:

^\d+$

Positive integers of maximum length (10 in our example):

^\d{1,10}$

Positive integers of fixed length (5 in our example):

^\d{5}$

Negative integers of undefined length:

^-\d+$

Negative integers of maximum length (10 in our example):

^-\d{1,10}$

Negative integers of fixed length (5 in our example):

^-\d{5}$

Integers of undefined length:

^-?\d+$

Integers of maximum length (10 in our example):

^-?\d{1,10}$

Integers of fixed length (5 in our example):

^-?\d{5}$

Numbers of undefined length with or without decimals (1234.1234):

^-?\d*\.{0,1}\d+$

Numbers with 2 decimals (.00):

^-?\d*\.\d{2}$

Currency numbers with optional dollar sign and thousand separators and optional 2 decimals ($1,000,00.00, 10000.12, 0.00):

^$?\-?([1-9]{1}[0-9]{0,2}(\,\d{3})*(\.\d{0,2})?|[1-9]{1}\d{0,}(\.\d{0,2})?|0(\.\d{0,2})?|(\.\d{1,2}))$|^\-?$?([1-9]{1}\d{0,2}(\,\d{3})*(\.\d{0,2})?|[1-9]{1}\d{0,}(\.\d{0,2})?|0(\.\d{0,2})?|(\.\d{1,2}))$|^\($?([1-9]{1}\d{0,2}(\,\d{3})*(\.\d{0,2})?|[1-9]{1}\d{0,}(\.\d{0,2})?|0(\.\d{0,2})?|(\.\d{1,2}))\)$

Percentage from 0 to 100 with optional 2 decimals and optional % sign at the end (0, 0.00, 100.00, 100%, 99.99%):

^-?[0-9]{0,2}(\.[0-9]{1,2})?%?$|^-?(100)(\.[0]{1,2})?%?$