Syntax

Symbol	Function
[\^$.\|?*+()	Special characters any other will match themselves
\	Escapes special characters and treat as literal
*	Repeat the previous item zero or more times
.	Single character except line break characters
.*	Match zero or more characters
^	Match at the start of a line/string
$	Match at the end of a line/string
.$	Match a single character at the end of line/string
^ $	Match line with a single space
[^A-Z]	Match any line beginning with any char from A to Z

Examples

For IP Addresses:

1. To Match upto 999.999.999.999:

\b\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}\b

OR shortened with a quantifier to:

\b(?:\d{1,3}\.){3}\d{1,3}\b

2. To match exactly upto 255.255.255.255:

 
\b(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b

OR shortened with a quantifier to:

\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b

For Credit Card numbers:

1. Visa card numbers start with a 4. New cards have 16 digits. Old cards have 13:

^4[0-9]{12}(?:[0-9]{3})?$

2. MasterCard numbers start with the numbers 51 through 55. All have 16 digits:

^5[1-5][0-9]{14}$

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