Regular Expression Cheat Sheet

Below is a quick reference guide for regular expressions that I frequently use and find useful.

Online RegEx debugger and library – https://regex101.com/

	# Validate Base64 string.
	[0-9a-zA-Z\+=]{20,}

	# Validate Subnet in CIDR notation.
	^(([01]?\d?\d\|2[0-4]\d\|25[0-5])\.){3}([01]?\d?\d\|2[0-4]\d\|25[0-5])\/(\d{1}\|[0-2]{1}\d{1}\|3[0-2])$

	# Validate IP address range.
	^(25[0-5]\|2[0-4][0-9]\|1[0-9][0-9]\|[0-9]{1,2})(\.(25[0-5]\|2[0-4][0-9]\|1[0-9][0-9]\|[0-9]{1,2})){3}-(25[0-5]\|2[0-4][0-9]\|1[0-9][0-9]\|[0-9]{1,2})(\.(25[0-5]\|2[0-4][0-9]\|1[0-9][0-9]\|[0-9]{1,2})){3}$

	# Validate IP address.
	^(25[0-5]\|2[0-4][0-9]\|1[0-9][0-9]\|[0-9]{1,2})(\.(25[0-5]\|2[0-4][0-9]\|1[0-9][0-9]\|[0-9]{1,2})){3}$

	# Validate an email address.
	\b[A-Z0-9._%+-]+@(?:[A-Z0-9-]+\.)+[A-Z]{2,4}\b

	# Validate an email address (RFC 5322 official definition)
	(?:[a-z0-9!#$%&'+/=?^_`{\|}~-]+(?:\.[a-z0-9!#$%&'+/=?^_`{\|}~-]+)*
	\| "(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]
	\| \\[\x01-\x09\x0b\x0c\x0e-\x7f])*")
	@ (?:(?:[a-z0-9](?:[a-z0-9-][a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-][a-z0-9])?
	\| \[(?:(?:25[0-5]\|2[0-4][0-9]\|[01]?[0-9][0-9]?)\.){3}
	(?:25[0-5]\|2[0-4][0-9]\|[01]?[0-9][0-9]?\|[a-z0-9-]*[a-z0-9]:
	(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]
	\| \\[\x01-\x09\x0b\x0c\x0e-\x7f])+)
	\])

	# Retrieve index from Win32_LogicalDiskToPartition antecedent.
	(?<=Disk #).+(?=\,)

	# Retrieve response header containing YouTrack issue number (New-YouTrackItem).
	[^/]+$