$isalpha(<text>)
$isdigit(<text>)

These function test whether the first character in the given string is an alphabetical character or a digit. Only the first character is tested.

These functions are useful for testing an input string to see whether it is a number or a text string. One use for this might be to check if it would be suitable input for $iptoname() or $nametoip(). Keep in mind that only the first character is tested, so this isn't a reliable way to see if the entire string is a number.

“true” or “false” value if first character is a letter or a digit

$isalpha(hello)         returns true
$isalpha(2hello)        returns false
$isdigit(123)           returns true
$isdigit(2abc)          returns true
$isdigit(a123)          returns false