Perl is jokingly referred to as a write-only language. This is because Perls primary solution to any problem is to throw a regular expression at it. Regexes are powerful, but cryptic.

Imagine RJs joy at starting a new contract for an OCR/document-management system that makes heavy use of regexes. Even better, the system doesnt use widely implemented Perl-compatible regular expressions syntax, but instead, uses its own, slightly tweaked version.

So, for example, when the system needs to pick the document ID out of the scanned document, it uses this regex:

([:-.,;/\\(]{0,2}(( [C|c][P|p][K,<|k,<][0-9]{11} )||([:#.$",'#-/|][C|c][P|p][K,<|k,<][0-9]{11} )||( [C|c][P|p][K,<|k,<][0-9]{11}[:.$",'#-/|l\\])||([:.$",'#-/|][C|c][P|p][K,<|k,<][0-9]{11}[:.$",'#-/|l\\])||( 01[A|a|C|c|D|d|E|e|R|r][0-9]{7} )||([:#.$",'#-/|]01[A|a|C|c|D|d|E|e|R|r][0-9]{7} )||(01[A|a|C|c|D|d|E|e|R|r][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]01[A|a|C|c|D|d|E|e|R|r][0-9]{7}[:#.$",'#-/|l\\])||( 02[A|a|B|b|C|c|D|d|E|e|F|f][0-9]{7} )||([:#.$",'#-/|]02[A|a|B|b|C|c|D|d|E|e|F|f][0-9]{7} )||( 02[A|a|B|b|C|c|D|d|E|e|F|f][0-9]{7}[:#.$",'#-/|l\\])||([:#-/|]02[A|a|B|b|C|c|D|d|E|e|F|f][0-9]{7}[:#.$",'#-/|l\\])||( 04[C|c|D|d|F|f|V|v][0-9]{7} )||([:#.$",'#-/|]04[C|c|D|d|F|f|V|v][0-9]{7} )||( 04[C|c|D|d|F|f|V|v][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]04[C|c|D|d|F|f|V|v][0-9]{7}[:#.$",'#-/|l\\])||( 05[M|m|A|a][0-9]{7} )||([:#.$",'#-/|]05[M|m|A|a][0-9]{7} )||( 05[M|m|A|a][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]05[M|m|A|a][0-9]{7}[:#.$",'#-/|l\\])||( 06[B|b|C|c|G|g|H|h|J|j|K|k|L|l|M|m|S|s|U|u|Y|y][0-9]{7} )||([:#.$",'#-/|]06[B|b|C|c|G|g|H|h|J|j|K|k|L|l|M|m|S|s|U|u|Y|y][0-9]{7} )||( 06[B|b|C|c|G|g|H|h|J|j|K|k|L|l|M|m|S|s|U|u|Y|y][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]06[B|b|C|c|G|g|H|h|J|j|K|k|L|l|M|m|S|s|U|u|Y|y][0-9]{7}[:#.$",'#-/|l\\])||( 07[U|u][0-9]{7} )||([:#.$",'#-/|]07[U|u][0-9]{7} )||( 07[U|u][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]07[U|u][0-9]{7}[:#.$",'#-/|l\\])||( 08[A|a][0-9]{7} )||([:#.$",'#-/|]08[A|a][0-9]{7} )||( 08[A|a][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]08[A|a][0-9]{7}[:#.$",'#-/|l\\])||( 09[A|a|B|b|C|c|D|d|F|f][0-9]{7} )||([:#.$",'#-/|]09[A|a|B|b|C|c|D|d|F|f][0-9]{7} )||( 09[A|a|B|b|C|c|D|d|F|f][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]09[A|a|B|b|C|c|D|d|F|f][0-9]{7}[:#.$",'#-/|l\\])||( 10[M|m|F|f][0-9]{7} )||([:#.$",'#-/|]10[M|m|F|f][0-9]{7} )||( 10[M|m|F|f][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]10[M|m|F|f][0-9]{7}[:#.$",'#-/|l\\])||( 13[A|a][0-9]{7} )||([:#.$",'#-/|]13[A|a][0-9]{7} )||( 13[A|a][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]13[A|a][0-9]{7}[:#.$",'#-/|l\\])||( 14[A|a][0-9]{7} )||([:#.$",'#-/|]14[A|a][0-9]{7} )||( 14[A|a][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]14[A|a][0-9]{7})||( 15[D|d|E|e|R|r|T|t][0-9]{7} )||([:#.$",'#-/|]15[D|d|E|e|R|r|T|t][0-9]{7} )||( 15[D|d|E|e|R|r|T|t][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]15[D|d|E|e|R|r|T|t][0-9]{7}[:#.$",'#-/|l\\])||( 17[A|a|E|e|L|l|M|m|P|p|S|s|U|u|W|w][0-9]{7} )||([:#.$",'#-/|]17[A|a|E|e|L|l|M|m|P|p|S|s|U|u|W|w][0-9]{7} )||( 17[A|a|E|e|L|l|M|m|P|p|S|s|U|u|W|w][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]17[A|a|E|e|L|l|M|m|P|p|S|s|U|u|W|w][0-9]{7}[:#.$",'#-/|l\\])||( 18[A|a][0-9]{7} )||([:#.$",'#-/|]18[A|a][0-9]{7} )||( 18[A|a][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]18[A|a][0-9]{7}[:#.$",'#-/|l\\])||( 21[A|a|C|c|D|d][0-9]{7} )||([:#.$",'#-/|]21[A|a|C|c|D|d][0-9]{7} )||( 21[A|a|C|c|D|d][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]21[A|a|C|c|D|d][0-9]{7}[:#.$",'#-/|l\\])||( 23[A|a|B|b|C|c|D|d|L|l|M|m][0-9]{7} )||([:#.$",'#-/|]23[A|a|B|b|C|c|D|d|L|l|M|m][0-9]{7} )||(23[A|a|B|b|C|c|D|d|L|l|M|m][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]23[A|a|B|b|C|c|D|d|L|l|M|m][0-9]{7}[:#.$",'#-/|l\\])
||( 24[A|a|B|b|C|c|F|f|K|k|M|m|T|t][0-9]{7} )||([:#.$",'#-/|]24[A|a|B|b|C|c|F|f|K|k|M|m|T|t][0-9]{7} )||( 24[A|a|B|b|C|c|F|f|K|k|M|m|T|t][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]24[A|a|B|b|C|c|F|f|K|k|M|m|T|t][0-9]{7}[:#.$",'#-/|l\\])
||( 25[A|a][0-9]{7} )||([:#.$",'#-/|]25[A|a][0-9]{7} )||( 25[A|a][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]25[A|a][0-9]{7}[:#.$",'#-/|l\\])||( 32[A|a|F|f|H|h|X|x|Y|y|Z|z][0-9]{7} )||([:#.$",'#-/|]32[A|a|F|f|H|h|X|x|Y|y|Z|z][0-9]{7} )||( 32[A|a|F|f|H|h|X|x|Y|y|Z|z][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]32[A|a|F|f|H|h|X|x|Y|y|Z|z][0-9]{7}[:#.$",'#-/|l\\])||( 34[A|a][0-9]{7} )||([:#.$",'#-/|]34[A|a][0-9]{7} )||( 34[A|a][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]34[A|a][0-9]{7}[:#.$",'#-/|l\\])
||( 35[A|a|B|R|r|S|s|T|t|U|u][0-9]{7} )||([:#.$",'#-/|]35[A|a|B|R|r|S|s|T|t|U|u][0-9]{7} )||( 35[A|a|B|R|r|S|s|T|t|U|u][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]35[A|a|B|R|r|S|s|T|t|U|u][0-9]{7}[:#.$",'#-/|l\\])||( 39[C|c|P|p][0-9]{7} )||([:#.$",'#-/|]39[C|c|P|p][0-9]{7} )||( 39[C|c|P|p][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]39[C|c|P|p][0-9]{7}[:#.$",'#-/|l\\])||( 40[A|a|C|c|D|d|S|s][0-9]{7} )||([:#.$",'#-/|]40[A|a|C|c|D|d|S|s][0-9]{7} )||( 40[A|a|C|c|D|d|S|s][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]40[A|a|C|c|D|d|S|s][0-9]{7}[:#.$",'#-/|l\\])||( 46[A|a|B|b][0-9]{7} )||([:#.$",'#-/|]46[A|a|B|b][0-9]{7} )||( 46[A|a|B|b][0-9]{7}[:#.$",'#-/|l\\])||([:#.$",'#-/|]46[A|a|B|b][0-9]{7}[:#.$",'#-/|l\\])
||( 01[A|a|C|c|D|d|E|e|R|r][0-9]{9} )||([:#.$",'#-/|]01[A|a|C|c|D|d|E|e|R|r][0-9]{9} )||(01[A|a|C|c|D|d|E|e|R|r][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]01[A|a|C|c|D|d|E|e|R|r][0-9]{9}[:#.$",'#-/|l\\])||( 02[A|a|B|b|C|c|D|d|E|e|F|f][0-9]{9} )
||([:#.$",'#-/|]02[A|a|B|b|C|c|D|d|E|e|F|f][0-9]{9} )||( 02[A|a|B|b|C|c|D|d|E|e|F|f][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]02[A|a|B|b|C|c|D|d|E|e|F|f][0-9]{9}[:#.$",'#-/|l\\])
||( 04[C|c|D|d|F|f|V|v][0-9]{9} )||([:#.$",'#-/|]04[C|c|D|d|F|f|V|v][0-9]{9} )||( 04[C|c|D|d|F|f|V|v][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]04[C|c|D|d|F|f|V|v][0-9]{9}[:#.$",'#-/|l\\])||( 05[M|m|A|a][0-9]{9} )||([:#.$",'#-/|]05[M|m|A|a][0-9]{9} )||( 05[M|m|A|a][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]05[M|m|A|a][0-9]{9}[:#.$",'#-/|l\\])||( 06[B|b|C|c|G|g|H|h|J|j|K|k|L|l|M|m|S|s|U|u|Y|y][0-9]{9} )||([:#.$",'#-/|]06[B|b|C|c|G|g|H|h|J|j|K|k|L|l|M|m|S|s|U|u|Y|y][0-9]{9} )||( 06[B|b|C|c|G|g|H|h|J|j|K|k|L|l|M|m|S|s|U|u|Y|y][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]06[B|b|C|c|G|g|H|h|J|j|K|k|L|l|M|m|S|s|U|u|Y|y][0-9]{9}[:#.$",'#-/|l\\])||( 07[U|u][0-9]{9} )||([:#.$",'#-/|]07[U|u][0-9]{9} )||( 07[U|u][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]07[U|u][0-9]{9}[:#.$",'#-/|l\\])||( 08[A|a][0-9]{9} )||([:#.$",'#-/|]08[A|a][0-9]{9} )||( 08[A|a][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]08[A|a][0-9]{9}[:#.$",'#-/|l\\])||( 09[A|a|B|b|C|c|D|d|F|f][0-9]{9} )||      ([:#.$",'#-/|]09[A|a|B|b|C|c|D|d|F|f][0-9]{9} )||( 09[A|a|B|b|C|c|D|d|F|f][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]09[A|a|B|b|C|c|D|d|F|f][0-9]{9}[:#.$",'#-/|l\\])||( 10[M|m|F|f][0-9]{9} )||([:#.$",'#-/|]10[M|m|F|f][0-9]{9} )||( 10[M|m|F|f][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]10[M|m|F|f][0-9]{9}[:#.$",'#-/|l\\])||( 13[A|a][0-9]{9} )||([:#.$",'#-/|]13[A|a][0-9]{9} )||( 13[A|a][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]13[A|a][0-9]{9}[:#.$",'#-/|l\\])||( 14[A|a][0-9]{9} )||
([:#.$",'#-/|]14[A|a][0-9]{9} )||( 14[A|a][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]14[A|a][0-9]{9}[:#.$",'#-/|l\\])|| ( 15[D|d|E|e|R|r|T|t][0-9]{9} )||([:#.$",'#-/|]15[D|d|E|e|R|r|T|t][0-9]{9} )||( 15[D|d|E|e|R|r|T|t][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]15[D|d|E|e|R|r|T|t][0-9]{9}[:#.$",'#-/|l\\])||( 17[A|a|E|e|L|l|M|m|P|p|S|s|U|u|W|w][0-9]{9} )||([:#.$",'#-/|]17[A|a|E|e|L|l|M|m|P|p|S|s|U|u|W|w][0-9]{9} )||( 17[A|a|E|e|L|l|M|m|P|p|S|s|U|u|W|w][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]17[A|a|E|e|L|l|M|m|P|p|S|s|U|u|W|w][0-9]{9}[:#.$",'#-/|l\\])||( 18[A|a][0-9]{9} )||([:#.$",'#-/|]18[A|a][0-9]{9} )||( 18[A|a][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]18[A|a][0-9]{9}[:#.$",'#-/|l\\])
||( 21[A|a|C|c|D|d][0-9]{9} )||([:#.$",'#-/|]21[A|a|C|c|D|d][0-9]{9} )||( 21[A|a|C|c|D|d][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]21[A|a|C|c|D|d][0-9]{9}[:#.$",'#-/|l\\])||( 23[A|a|B|b|C|c|D|d|L|l|M|m][0-9]{9} )||([:#.$",'#-/|]23[A|a|B|b|C|c|D|d|L|l|M|m][0-9]{9} )||( 23[A|a|B|b|C|c|D|d|L|l|M|m][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]23[A|a|B|b|C|c|D|d|L|l|M|m][0-9]{9}[:#.$",'#-/|l\\])||( 24[A|a|B|b|C|c|F|f|K|k|M|m|T|t][0-9]{9} )||([:#.$",'#-/|]24[A|a|B|b|C|c|F|f|K|k|M|m|T|t][0-9]{9} )||( 24[A|a|B|b|C|c|F|f|K|k|M|m|T|t][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]24[A|a|B|b|C|c|F|f|K|k|M|m|T|t][0-9]{9}[:#.$",'#-/|l\\])||( 25[A|a][0-9]{9} )||([:#.$",'#-/|]25[A|a][0-9]{9} )||( 25[A|a][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]25[A|a][0-9]{9}[:#.$",'#-/|l\\])
||( 32[A|a|F|f|H|h|X|x|Y|y|Z|z][0-9]{9} )||([:#.$",'#-/|]32[A|a|F|f|H|h|X|x|Y|y|Z|z][0-9]{9} )||( 32[A|a|F|f|H|h|X|x|Y|y|Z|z][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]32[A|a|F|f|H|h|X|x|Y|y|Z|z][0-9]{9}[:#.$",'#-/|l\\])||( 34[A|a][0-9]{9} )||([:#.$",'#-/|]34[A|a][0-9]{9} )||( 34[A|a][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]34[A|a][0-9]{9}[:#.$",'#-/|l\\])||( 35[A|a|B|b|R|r|S|s|T|t|U|u][0-9]{9} )||([:#.$",'#-/|]35[A|a|B|b|R|r|S|s|T|t|U|u][0-9]{9} )||( 35[A|a|B|b|R|r|S|s|T|t|U|u][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]35[A|a|B|b|R|r|S|s|T|t|U|u][0-9]{9}[:#.$",'#-/|l\\])||( 39[C|c|P|p][0-9]{9} )||([:#.$",'#-/|]39[C|c|P|p][0-9]{9} )||( 39[C|c|P|p][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]39[C|c|P|p][0-9]{9}[:#.$",'#-/|l\\])
||( 40[A|a|C|c|D|d|S|s][0-9]{9} )||([:#.$",'#-/|]40[A|a|C|c|D|d|S|s][0-9]{9} )||( 40[A|a|C|c|D|d|S|s][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]40[A|a|C|c|D|d|S|s][0-9]{9}[:#.$",'#-/|l\\])||( 46[A|a|B|b][0-9]{9} )||([:#.$",'#-/|]46[A|a|B|b][0-9]{9} )||( 46[A|a|B|b][0-9]{9}[:#.$",'#-/|l\\])||([:#.$",'#-/|]46[A|a|B|b][0-9]{9}[:#.$",'#-/|l\\]))[-.,;:Il|/\\]{0,2} )

RJ added, Given the scale of WTF in this place, I was only mildly surprised such an abomination existed. I share it for your amusement. If this is only a mild surprise, RJ, may the gods have mercy on your soul.

http://thedailywtf.com/articles/regularly-expressing-hate