The document discusses regular expressions (regex or regexp). It begins with definitions of regex from a mathematical and programming perspective. It then covers topics like Unicode support, nested parentheses, modifiers, and libraries like Regexp::Common that provide common regex patterns.

1. @dankogai
my$talk=qr{((?:ir)?reg(?:ular )?
exp(?:ressions?)?)}i;

2. Table of Contents
• regexp? what is it?
• $supported_by ~~ @most_major_languages;
• but how (much)??
• Unicode support?
• assertions?
• modifiers?
• Irregular expressions
• qr{([A-Za-z_]w*s*((((?:(?>[^()]+)|(?2))*))))}
• use CPAN;
• Regexp::Assemble;
• Regexp::Common;
• (ir)?regular questions (?:from|by) the audience

3. regexp? what is it?
Mathematically speaking[*]
• The empty language Ø is a regular language.
• For each a ∈ Σ (a belongs to Σ), the singleton language {a} is a regular
language.
• If A is a regular language, A* (Kleene star) is a regular language. Due to this,
the empty string language {ε} is also regular.
• If A and B are regular languages, then A ∪ B (union) and A • B (concatenation)
are regular languages.
• No other languages over Σ are regular.

4. regexp? what is it?
In our language
• 0 or more of… (quantifier)
• '' # empty string
• 'string' # any string
• '(?:string|文字列)' # any alteration of strings
• That's it!
• ? # {0,}
• + # {1,}
• [0-9] # (?:0|1|2|3|4|5|6|7|8|9)

5. regexp? what is it?
((?:ir)?reg(?:ular )?exp(?:ressions?)?)
Visualized by: regexper.com

6. regexp? what is it?
(?:[x00-x7F]|[xC2-xDF][x80-xBF]|xE0[xA0-xBF][x80-xBF]|[xE1-xECxEExEF][x80-xBF]{2}|xED[x80-x9F][x80-xBF]|
xF0[x90-xBF][x80-xBF]{2}|[xF1-xF3][x80-xBF]{3}|xF4[x80-x8F][x80-xBF]{2})
Exerpt from: https://www.w3.org/International/questions/qa-forms-utf-8
Visualized by: regexper.com

7. regexp? what is it?
(?:[+-]?)(?:0x[0-9a-fA-F]+(?:.[0-9a-fA-F]+)?(?:[pP][+-]?[0-9]+)|(?:[1-9][0-9]*)(?:.[0-9]+)?(?:[eE][+-]?[0-9]+)?|0(?:.0+|(?:.0+)?(?:[eE]
[+-]?[0-9]+))|(?:[Nn]a[Nn]|[Ii]nf(?:inity)?))
Exerpt from: https://github.com/dankogai/js-sion/blob/main/sion.ts
Visualized by: regexper.com

8. Irregular expressions
/^(11+?)1+$/ # is this a regular expression?
$ seq 2 100 | perl -nlE 'say $_ if (1x$_) !~ /^(11+?)1+$/'

9. Irregular expressions
/^(11+?)1+$/ # is this a regular expression?
$ seq 2 100 | perl -nlE 'say $_ if (1x$_) !~ /^(11+?)1+$/'
2
3
5
7
…
79
83
89
97

10. Irregular expressions
/^(11+?)1+$/ # is NOT EXACTLY a regular expression!
• The problem is 1
• It is the result of the preceding capture
• In other words, this expression is self-modifying.
• So it is not mathematically a regular expression
• Regexp ≠ Regular Expression
• Regexp ⊆ Regular Expression

11. Irregular expressions
qr{([A-Za-z_]w*s*((((?:(?>[^()]+)|(?2))*))))}
• Q: Can a regular expression match nested parentheses?
• A: No. But some regex engines allow you to do that.

12. Irregular expressions
qr{([A-Za-z_]w*s*((((?:(?>[^()]+)|(?2))*))))}
my $re = qr{(
[A-Za-z_]w*s*
(
(
(
(?:
(?>[^()]+)
|
(?2)
)*
)
)
)
)
}x;

13. Irregular expressions
qr{([A-Za-z_]w*s*((((?:(?>[^()]+)|(?2))*))))}
#!/usr/bin/env perl
use strict;
use warnings;
use feature ':all';
my $re = qr{([A-Za-z_]w*s*((((?:(?>[^()]+)|(?2))*))))};
my $str = '$result = a(b(c),d(e,f(g,g,g)))';
$str =~ $re;
say $1;
say $2;
say $3;

14. Unicode Support
What is a character?
• String is /.*/ but . =
• [x00-xff] # legacy world of bytes
• [u0000-uFFFF] # prematurely modern
• [u{0000}-u{10FFFF}] # correctly modern

15. Unicode Support
What is a character?
• String is /.*/ but . =
• [x00-xff] # Perl < 5.7
• [u0000-uFFFF] # Java(Script)?, Python2, …
• [u{0000}-u{10FFFF}] # Perl, Ruby, Python3, …

16. Unicode Support?
What will the following say?
$ perl -Mutf8 -MData::Dumper -E
'my@m=("🦏🐪🐘🐍💎⚙" =~ /(.)/g); say Dumper([@m])'

17. Unicode Support?
What will the following say?
$ perl -Mutf8 -MData::Dumper -E
'my@m=("🦏🐪🐘🐍💎⚙" =~ /(.)/g); say Dumper([@m])'
$VAR1 = [
"x{1f98f}",
"x{1f42a}",
"x{1f418}",
"x{1f40d}",
"x{1f48e}",
"x{2699}"
];

18. Unicode Support?
What will the following say?
$ node -e
'console.log("🦏🐪🐘🐍💎⚙".match(/(.)/g))'

19. Unicode Support?
What will the following say?
$ node -e
'console.log("🦏🐪🐘🐍💎⚙".match(/(.)/g))'
[
'', '', '', '',
'', '', '', '',
'', '', '⚙'
]

20. Unicode Support?
What will the following say?
$ node -e
'console.log("🦏🐪🐘🐍💎⚙".match(/(.)/ug))'
[ '🦏', '🐪', '🐘', '🐍', '💎', '⚙' ]

21. Unicode Support?
What will the following say?
$ perl -Mutf8 -MData::Dumper -E
'my@m=("🇯🇵🇺🇦" =~ /(.)/g); say Dumper([@m])'

22. Unicode Support?
What will the following say?
$ perl -Mutf8 -MData::Dumper -E
'my@m=("🇯🇵🇺🇦" =~ /(.)/g); say Dumper([@m])'
$VAR1 = [
"x{1f1ef}",
"x{1f1f5}",
"x{1f1fa}",
"x{1f1e6}"
];

23. Unicode Support?
What will the following say?
$ perl -Mutf8 -MData::Dumper -E
'my@m=("🇯🇵🇺🇦" =~ /(.)/g); say Dumper([@m])'
$VAR1 = [
"x{1f1ef}", # REGIONAL INDICATOR SYMBOL LETTER J
"x{1f1f5}", # REGIONAL INDICATOR SYMBOL LETTER P
"x{1f1fa}", # REGIONAL INDICATOR SYMBOL LETTER U
"x{1f1e6}" # REGIONAL INDICATOR SYMBOL LETTER A
];

24. Unicode Support?
What will the following say?
$ perl -Mutf8 -MData::Dumper -E
'my@m=("🇯🇵🇺🇦" =~ /(X)/g); say Dumper([@m])'
$VAR1 = [
"x{1f1ef}x{1f1f5}",
"x{1f1fa}x{1f1e6}"
];

25. Unicode Support?
What will the following say?
$ node -e
'console.log("🇯🇵🇺🇦".match(/(.)/ug))'

26. Unicode Support?
What will the following say?
$ node -e
'console.log("🇯🇵🇺🇦".match(/(.)/ug))'
[ '🇯', '🇵', '🇺', '🇦' ]

27. Unicode Support?
What will the following say?
$ node -e
'console.log("🇯🇵🇺🇦".match(/(X)/ug))'
🙅 [ '🇯🇵','🇺🇦' ]
🙆 SyntaxError: Invalid regular expression: /(X)/: Invalid escape
at [eval]:1:24
at Script.runInThisContext (node:vm:129:12)
at Object.runInThisContext (node:vm:305:38)
at node:internal/process/execution:75:19
at [eval]-wrapper:6:22
at evalScript (node:internal/process/execution:74:60)
at node:internal/main/eval_string:27:3

28. 🤦

29. Unicode Support?
Grapheme Cluster
• Defined in:
• https://unicode.org/reports/tr29/
• X is supported by:
• 🐘 PHP
• 🐪 Perl
• 💎 Ruby
• Not yet supported by:
• 🦏 JavaScript
• 🐍 Python

30. use CPAN
Regexp::Common
$ perl -MRegexp::Common -E 'say $RE{net}{IPv6}'

31. use CPAN
Regexp::Common
$perl -MRegexp::Common -E 'say $RE{net}{IPv6}'
(?:(?|(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-
fA-F]{1,4})|(?::(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?::(?:)(?:)(?:):
(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?::(?:)(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]
{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?::(?:)(?:)(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?::(?:)(?:)(?:)(?:)(?:)(?:):(?:
[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?::(?:)(?:)(?:)(?:)(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}))|(?::(?:)(?:)(?:)(?:)(?:)(?:)(?:)(?:):)|(?:(?:[0-9a-fA-F]{1,4}):(?:)(?:):(?:[0-9a-
fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-
fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?:(?:
[0-9a-fA-F]{1,4}):(?:)(?:)(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:)(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]
{1,4}):(?:)(?:)(?:)(?:)(?:)(?:)(?:):)|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]
{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-
F]{1,4}):(?:)(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-
fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:)(?:)(?:)(?:):)|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-
F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-
fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:)
(?:)(?:)(?:):)|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-
fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:):(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-
fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:)(?:):)|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:):
(?:[0-9a-fA-F]{1,4}))|(?:(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:)(?:):)|(?:(?:[0-9a-fA-F]
{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:[0-9a-fA-F]{1,4}):(?:)(?:):)))

32. use CPAN
Regexp::Assemble
$ egrep '^.{5}$' /usr/share/dict/words
| perl -MRegexp::Assemble -nl
-E 'BEGIN{$ra=Regexp::Assemble->new}'
-E '$ra->add($_);'
-E 'END{say $ra->re}'

33. Wrap↑
• (?:ir)?regular expressions
• Regexp ≠ Regular Expression
• Regexp ⊆ Regular Expression
• Definition of characters
• [x00-xff]
• [u0000-uFFFF]
• [u{0000}-u{10FFFF}]
• (?:un)?availability of X
• Using perl? use CPAN!

34. BTW
Bible, an obsolete
• 3rd edition: August 8,
2006
• Too old especially for
JS

35. Thank you
🙇

36. Questions and answers
answer($_) foreach (/($questions)/sg);