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).
[^/]+$


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