Answers for "regex from numbers"

regex 10 numbers only

@"^d{10}$"

regex match number

For matching an integer number of one single char/digit, specify:
[0-9]
But for matching any number of more than one char/digit; add "+":
[0-9]+
Example for matching hour with minutes of HH:MM format in a file:
grep "[0-9]+:[0-9]+" file.txt