Perl Differences

The differences described here are with respect to Perl 5.005.

  1. By default, a whitespace character is any character that the C library function isspace() recognizes, though it is possible to compile PCRE with alternative character type tables. Normally isspace() matches space, formfeed, newline, carriage return, horizontal tab, and vertical tab. Perl 5 no longer includes vertical tab in its set of whitespace characters. The \v escape that was in the Perl documentation for a long time was never in fact recognized. However, the character itself was treated as whitespace at least up to 5.002. In 5.004 and 5.005 it does not match \s.
  2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl permits them, but they do not mean what you might think. For example, (?!a) does not assert that the next three characters are not "a". It just asserts that the next character is not "a" three times.
  3. Capturing subpatterns that occur inside negative lookahead assertions are counted, but their entries in the offsets vector are never set. Perl sets its numerical variables from any such patterns that are matched before the assertion fails to match something (thereby succeeding), but only if the negative lookahead assertion contains just one branch.
  4. Though binary zero characters are supported in the subject string, they are not allowed in a pattern string because it is passed as a normal C string, terminated by zero. The escape sequence "\x00" can be used in the pattern to represent a binary zero.
  5. The following Perl escape sequences are not supported: \l, \u, \L, \U. In fact these are implemented by Perl's general string-handling and are not part of its pattern matching engine.
  6. The Perl \G assertion is not supported as it is not relevant to single pattern matches.
  7. Fairly obviously, PCRE does not support the (?) and (??) construction. However, there is support for recursive patterns.
  8. There are at the time of writing some oddities in Perl 5.005_02 concerned with the settings of captured strings when part of a pattern is repeated. For example, matching "aba" against the pattern /^(a(b)?)+$/ sets $2 to the value "b", but matching "aabbaa" against /^(aa(bb)?)+$/ leaves $2 unset. However, if the pattern is changed to /^(aa(b(b))?)+$/ then $2 (and $3) get set. In Perl 5.004 $2 is set in both cases, and that is also true of PCRE. If in the future Perl changes to a consistent state that is different, PCRE may change to follow.
  9. Another as yet unresolved discrepancy is that in Perl 5.005_02 the pattern /^(a)?(?(1)a|b)+$/ matches the string "a", whereas in PCRE it does not. However, in both Perl and PCRE /^(a)?a/ matched against "a" leaves $1 unset.
  10. PCRE provides some extensions to the Perl regular expression facilities:

    1. Although lookbehind assertions must match fixed length strings, each alternative branch of a lookbehind assertion can match a different length of string. Perl 5.005 requires them all to have the same length.
    2. If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $ meta-character matches only at the very end of the string.
    3. If PCRE_EXTRA is set, a backslash followed by a letter with no special meaning is faulted.
    4. If PCRE_UNGREEDY is set, the greediness of the repetition quantifiers is inverted, that is, by default they are not greedy, but if followed by a question mark they are.

Hier Kannst Du einen Kommentar verfassen


Bitte gib mindestens 10 Zeichen ein.
Wird geladen... Bitte warte.
* Pflichtangabe
Es sind noch keine Kommentare vorhanden.

PHP cURL-Tutorial: Verwendung von cURL zum Durchführen von HTTP-Anfragen

cURL ist eine leistungsstarke PHP-Erweiterung, die es Ihnen ermöglicht, mit verschiedenen Servern über verschiedene Protokolle wie HTTP, HTTPS, FTP und mehr zu kommunizieren. ...

TheMax

Autor : TheMax
Kategorie: PHP-Tutorials

Midjourney Tutorial - Anleitung für Anfänger

Über Midjourney, dem Tool zur Erstellung digitaler Bilder mithilfe von künstlicher Intelligenz, gibt es ein informatives Video mit dem Titel "Midjourney Tutorial auf Deutsch - Anleitung für Anfänger" ...

Mike94

Autor : Mike94
Kategorie: KI Tutorials

Grundlagen von Views in MySQL

Views in einer MySQL-Datenbank bieten die Möglichkeit, eine virtuelle Tabelle basierend auf dem Ergebnis einer SQL-Abfrage zu erstellen. ...

admin

Autor : admin
Kategorie: mySQL-Tutorials

Tutorial veröffentlichen

Tutorial veröffentlichen

Teile Dein Wissen mit anderen Entwicklern weltweit

Du bist Profi in deinem Bereich und möchtest dein Wissen teilen, dann melde dich jetzt an und teile es mit unserer PHP-Community

mehr erfahren

Tutorial veröffentlichen

Spielgeschenk für Freund zu finden

Nun, was ist es, das Geschenk für sicher für 4 Jahre gefunden, oder müssen wir helfen?))))))))

Geschrieben von benisfroms am 31.10.2024 20:21:11
Forum: Off-Topic Diskussionen
Communicate with TELEGRAM Bot

Jacksmith (https://jacksmithgame.io) is a very cool and engaging action and strategy game. In this game, you will play as a talented blacksmith wh ...

Geschrieben von Eunicebayer am 31.10.2024 05:22:54
Forum: PHP Developer Forum
Wieder Kapazitäten frei!

CRM oder Customer Relationship Management (https://chudovo.de/projects/fdp-bundestagsfraktion-crm/) ist die Lösung, die die Analyse und Verwaltun ...

Geschrieben von oliv25menz am 30.10.2024 15:44:32
Forum: Archiv / Trash
übergabeproblem

To fix the radio button value transfer issue, ensure the variable name in PHP matches the Retro Bowl (https://retrobowl.college) name attribute in ...

Geschrieben von sabrina23 am 30.10.2024 08:50:33
Forum: PHP Developer Forum