Editing Computing (section)

== Regular Expressions ==

=== Resources ===

[https://regex101.com/ Regex101] site (very handy online checker and pretty)
[http://regexlib.com/ Regex Library]

=== IPv4 address examples ===
<pre>^(([1-9]|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.)((\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.){2}(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])$</pre>

Some test formats:

<pre>1.0.0.0 < - matches

0.0.0.0 <- no match

1.0.0.255 < - matches

1.01.0.255 < - no match

1.255.255.255 < - matches

1.256.255.255 < - no match

255.255.255.255 < - matches

256.255.255.255 < - no match</pre>

==== IPv4 with slash & network mask ====
<pre>
^(([1-9]|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.)((\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.){2}(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\/([1-9]|[1-2]\d|3[0-2])$</pre>

Some examples to test:
<pre>1.0.0.0/1 < - matches
1.0.0.255/30 < - matches
1.255.255.255/24 < - matches
255.255.255.255/10 < - matches
1.0.0.0/100 < - matches
1.0.0.255/0 < - no match</pre>

=== IPv6 address examples (hexadecimal formats only) ===

Long form only:

<pre>^([0-9a-fA-F]{4}:){7}[0-9a-fA-F]{4}$</pre>

Medium form that allows leading zeros in hextet:

<pre>^([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}$</pre>

Medium form that does not allow leading zeros in hextet:

<pre>^(([0-9a-fA-F]{1}|[1-9a-fA-F]{1}[0-9a-fA-F]{1,3}):){7}([0-9a-fA-F]{1}|[1-9a-fA-F]{1}[0-9a-fA-F]{1,3})$</pre>

Some test formats:
<pre>0:0:0:0:0:0:0:0

7:6:5:4:3:2:1:0

ffff:ffff:ffff:ffff:FFFF:FFFF:FFFF:FFFF

0fff:ffff:ffff:ffff:FFFF:FFFF:FFFF:FFFF (invalid due to leading 0 in first hextet group)</pre>

==== IPv6 with slash & network mask ====

<pre>(^(([0-9a-fA-F]{4}:){7}[0-9a-fA-F]{4})|(^([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}))\/([1-9]|[1-9]\d|1[0-1]\d|12[0-8])$</pre>

Some test formats:
<pre>0:0:0:0:0:0:0:0/69 < - matches
0:0:0:0:0:0:0:0/1 < - matches
7:6:5:4:3:2:1:0/10 < - matches
7:6:5:4:3:2:1:0/99 < - matches
7:6:5:4:3:2:1:0/128 < - matches
7:6:5:4:3:2:1:0/129 < - no match
7:6:5:4:3:2:1:0/0 < - no match
ffff:ffff:ffff:ffff:FFFF:FFFF:FFFF:FFFF/55 < - matches
fff:ffff:ffff:ffff:FFFF:FFFF:FFFF:FFFF/119 < - matches
2001:0db8:0000:0000:0000:ff00:0042:8329/0 < - no match
2001:0db8:0000:0000:0000:ff00:0042:8329/20 < - matches
2001:db8:0:0:0:ff00:42:8329/9 < - matches</pre>

=== IPv4 & IPv6 combined regex ===

I simply combined the above examples into one pattern that can match various formats. The following pattern matches both IPv4 and IPv6 addresses, both long and medium (allow leading zeros), using single regex:

<pre>(^(([0-9a-fA-F]{1,4}:){4,7}[0-9a-fA-F]{1,4})$)|(^([0-9a-fA-F]{4}:){7}[0-9a-fA-F]{4}$)|(^(([1-9]|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.)((\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.){2}(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])$)</pre>

==== IPv4 and IPv6 network and masks ====

<pre>(^(([0-9a-fA-F]{1,4}:){4,7}[0-9a-fA-F]{1,4})\/([1-9]|[1-9]\d|1[0-1]\d|12[0-8])$)|(^([0-9a-fA-F]{4}:){7}[0-9a-fA-F]{4}\/([1-9]|[1-9]\d|1[0-1]\d|12[0-8])$)|(^(([1-9]|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.)((\d|[1-9]\d|1\d\d|2[0-4]\d|25[0-5])\.){2}(\d{1,2}|1\d\d|2[0-4]\d|25[0-5])\/([1-9]|[1-9]\d|1[0-1]\d|12[0-8])$)</pre>

Some examples

<pre>0:0:0:0:0:0:0:0/1 < - matches
0:0:0:0:0:0:0:0/1 < - matches
7:6:5:4:3:2:1:0/10 < - matches
7:6:5:4:3:2:1:0/99 < - matches
7:6:5:4:3:2:1:0/128 < - matches
7:6:5:4:3:2:1:0/129 < - no match
7:6:5:4:3:2:1:0/0 < - no match
ffff:ffff:ffff:ffff:FFFF:FFFF:FFFF:FFFF/69 < - matches
fff:ffff:ffff:ffff:FFFF:FFFF:FFFF:FFFF/119 < - matches
2001:0db8:0000:0000:0000:ff00:0042:8329/0 < - no match
2001:db8:0:0:0:ff00:42:8329/9 < - matches
1.0.0.0/1 < - matches
1.0.0.255/30 < - matches
1.255.255.255/24 < - matches
255.255.255.255/10 < - matches
1.0.0.0/100 < - matches
1.0.0.255/0 < - no match</pre>

=== Ethernet MAC address examples ===

The following MAC address regex examples match lower or upper case hexadecimal values.

MAC address format using hyphen between each octet (default output for PowerShell)

<pre>^([0-9a-fA-F]{2}-){5}[0-9a-fA-F]{2}$

98-E7-43-D1-74-D4 < - matches</pre>

MAC address format using colon (default for Linux)

<pre>^([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}$

98:E7:43:-D1:74:D4 < - matches</pre>

MAC address format without any delimiters

<pre>^[0-9a-fA-F]{12}$

98E743D174D4 < - matches</pre>

Combine all three above regex to match any of three

<pre>(^([0-9a-fA-F]{2}-){5}[0-9a-fA-F]{2}$)|(^([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}$)|(^[0-9a-fA-F]{12}$)

98-E7-43-D1-74-D4 < - matches
98:E7:43:D1:74:D4 < - matches
98E743D174D4 < - matches</pre>

''Note that you must assert start and end characters within the groups above.''

If you use <code>^(([0-9a-fA-F]{2}-){5}[0-9a-fA-F]{2})|(([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2})|([0-9a-fA-F]{12})$</code> (assertions are outside groups) then invalid values would be matched:

<pre>98-E7-43-D1-74-D4
98-E7-43-D1-74-D40 < - invalid MAC, but matched regex

98:E7:43:D1:74:D4
98:E7:43:D1:74:D40 < - invalid MAC, but matched regex

98E743D174D4
98E743D174D40 < - invalid MAC, but matched regex</pre>

=== My regex notes for checking an ASN.1 GeneralizedTime type ===

'''General (my wording!)'''
* ^ means start of string
* () means capture everything inside
* | means or, aka "pipe" key
* [] means single character with rules, rules are inside square brackets
* \d means any digit
* {} means quantity with specified conditions
* ? means zero or one of previous character
* $ means end of string

Regex based on US requirements for time (within 200ms of event time) plus optional Z offset:

<code>^20(19|20)([0][1-9]|[1][0-2])([0][1-9]|[1-2][\d]|[3][0-1])([0-1][\d]|[2][0-4])([0-5][\d])([0-5][\d]).\d{1,3}Z?$</code>

Regex explained
* <code>^20(19|20)</code> = string starts with exactly 20 followed by 19 or 20 (match year "YYYY format")
* <code>([0][1-9]|[1][0-2])</code> = next two characters must match either [0][1-9] or [1][0-2], which means 01-09 or 10-12 (match month "MM format")
* <code>([0][1-9]|[1-2][\d]|[3][0-1])</code> = next two characters must match either [0][1-9] or [1-2][\d] or [3][0-1], which means 01-09 or 10-29 or 30-31(match day "DD format")
* <code>([0-1][\d]|[2][0-4])</code> = next two characters must match either [0][\d] or [1][\d] or [2][0-4], which means 00-09 or 10-19 or 20-24 (match hour "HH format" in 24-hour format)
* <code>([0-5][\d])</code> = next two characters must match [0-5][\d], which means 00-59 (match minutes "MM format")
* <code>([0-5][\d])</code> = next two characters must match [0-5][\d], which means 00-59 (match minutes "SS format")
* <code>.</code> = next character must be . (period)
* <code>\d{1,3}</code> = next 1 to 3 characters must be any digit (match milliseconds .f, .ff, .fff format)
* <code>Z?</code> = next character must be zero or one of Z (capital Z). Zero Z means Z is missing
* <code>$</code> = end of string (no following characters)</pre>

Take examples, like 20190822005901.9Z, 20190801230059.09Z, 20190822005901.991Z, and play around in [https://regex101.com/ Regex101] online tool

=== ISO 8601 Date and Time format ===

Date and time with UTC

<code>^2(\d\d\d)([0][1-9]|[1][0-2])([0][1-9]|[1-2][\d]|[3][0-1])T(([0-1][\d]|[2][0-3])([0-5][\d])([0-5][\d])|240000)Z?$</code>

This matches:
* 20231106T240000Z