正则表达式不返回预期数据
Regex not returning expected data
我有以下字符串 ($a) 并试图隔离从分隔符“|”开始的文本其中单词 "president" 直到下一个相同的分隔符“|”，我有以下代码，其中 returns 比预期更多的数据。
<?php
$a = '{{Redirect|Harvard}} {{pp-move-indef}} {{Use mdy dates|date=August
2014}} {{pp-semi-blp|small=yes}}{{Infobox university |name = Harvard
University |image_name = Harvard Wreath Logo 1.svg |image_size = |caption
= [[Seal (emblem)|Seal]] of Harvard University |latin_name = Universitas
Harvardiana |motto = ''Veritas''Harvard's ''Veritas'' appears on the
university's arms; [[Heraldry|heraldically]] speaking, however, a 'motto'
is a word or phrase displayed on a scroll in conjunction with a shield of
arms. [https://books.google.com/books?
id=zkQWZaZqZfUC&pg=PA330&lpg=PA330#v=onepage&q&f=false Since 1692]
University [[seal (device)|seals]] have borne ''Christo et Ecclesiae''
(for Christ and the Church) in this manner, arguably making that phrase
the university's motto in a heraldic sense. This legend is otherwise not
in general use today. |established = 1636An appropriation of £400 toward
a "school or college" was voted on October 28, 1636 (OS), at a meeting
which convened on September 8 and was adjourned to October 28. Some
sources consider October 28, 1636 (OS) (November 7, 1636 NS) to be the
date of founding. Harvard's 1936 tercentenary celebration treated
September 18 as the founding date, though 1836 bicentennial was
celebrated on September 8, 1836. Sources: meeting dates, {{cite
book|first=Josiah|last=Quincy|title=History of Harvard University
|year=1860 |publisher=Crosby, Nichols, Lee and Co.|location=117
Washington Street, Boston}}, [https://books.google.com/books?
vid=OCLC11636583&id=KynqxH_4lGUC&pg=RA1-PA586&lpg=RA1-PA586 p. 586], "At
a Court holden September 8th, 1636 and continued by adjournment to the
28th of the 8th month (October, 1636)... the Court agreed to give £400
towards a School or College, whereof £200 to be paid next year...."
Tercentenary dates: {{cite
news|url=http://www.time.com/time/
magazine/printout/0,8816,756722,00.html|date=September 28,
1936|accessdate=September 8, 2006|work=Time|title=Cambridge Birthday}}:
"Harvard claims birth on the day the Massachusetts Great and General
Court convened to authorize its founding. This was Sept. 8, 1637 under
the Julian calendar. Allowing for the ten-day advance of the Gregorian
calendar, Tercentenary officials arrived at Sept. 18 as the date for the
third and last big Day of the celebration;" "on Oct. 28, 1636 ... £400
for that 'school or college' [was voted by] the Great and General Court
of the [[Massachusetts Bay Colony]]." Bicentennial date: {{cite web
|url=http://www.news.harvard.edu/gazette/2003/10.02/02-
history.html|publisher=Harvard University|title=Harvard Gazette: This
Month in Harvard History|date=September 2, 2003 |accessdate=September 15,
2006|author=Marvin Hightower}}, "Sept. 8, 1836 - Some 1,100 to 1,300
alumni flock to Harvard's Bicentennial, at which a professional choir
premieres "Fair Harvard." ... guest speaker Josiah Quincy Jr., Class of
1821, makes a motion, unanimously adopted, 'that this assembly of the
Alumni be adjourned to meet at this place on September 8, 1936.'"
Tercentary opening of Quincy's sealed package: ''The New York Times,''
September 9, 1936, p. 24, "Package Sealed in 1836 Opened at Harvard. It
Held Letters Written at Bicentenary": "September 8th, 1936: As the first
formal function in the celebration of Harvard's tercentenary, the Harvard
Alumni Association witnessed the opening by President Conant of the
'mysterious' package sealed by President Josiah Quincy at the Harvard
bicentennial in 1836." |mottoeng = Truth |type = [[Private
university|Private]] – [[Research]] |calendar = Semester |endowment =
.4 billion{{As of|2014|06|30}}. {{cite web | title = Harvard Endowment
Earns 15.4% Return for Fiscal 2014| work = The Wall Street Journal | url
= http://online.wsj.com/articles/harvard-endowment-earns-15-4-return-for-
fiscal-2014-1411506002 | accessdate=10 October 2014}} |president = [[Drew
Gilpin Faust]] |students = 21,000{{As of|2014|09|01}}. {{cite web | title
= Harvard at a Glance| work = Harvard University | url =
http://www.harvard.edu/harvard-glance | accessdate=27 November 2014}}
|undergrad = 6,700 |postgrad = 14,500 |staff = |faculty = 4,671{{Cite
book|last=Office of Institutional Research.|title=Harvard University Fact
Book|year=2009|chapter=Faculty|url=http://
www.provost.harvard.edu/institutional_research/Provost_-_09_18-
19facuni.pdf}} ("Unduplicated, Paid Instructional Faculty Count: 2,107.
Unduplicated instructional faculty count is the most appropriate count
for general reporting purposes.") |city = [[Cambridge,
Massachusetts|Cambridge]] |state = [[Massachusetts]] |country = United
States |campus = [[Urban area|Urban]]{{Convert|210|acre|ha}} (Main
campus){{Convert|21|acre|ha}} (Medical campus)
{{Convert|360|acre|ha}} (Allston campus)
{{Convert|4500|acre|ha}} (other holdings) |sports = 42 varsity teams
|athletics = [[National Collegiate Athletic Association|NCAA]] [[Division
I (NCAA)|Division I]] – [[Ivy League]] |nickname = [[Harvard Crimson]]
|colors = {{color box|#A41034}} [[Crimson]]{{cite web|title=Color -
Identity Guidelines - Harvard Business
School|url=http://www.hbs.edu/marketing/color.html|publisher=Harvard
Business School|accessdate=26 September 2014}} |free_label = Student
newspaper |free = ''[[The Harvard Crimson]]'' |affiliations = [[National
Association of Independent Colleges and Universities|NAICU]]
[[Association of Independent Colleges and Universities in
Massachusetts|AICUM]][[Association of American Universities|AAU]]
[[Universities Research Association|URA]] |website =
{{URL|http://www.harvard.edu/|Harvard.edu}} |logo = [[File:Harvard
University logo.PNG|Harvard University logo (with its coat of arms)]]
|publictransit = [[Harvard (MBTA station)]] }} '''Harvard University'''
is a [[Private university|private]] [[Ivy League]] [[Doctoral
university|research university]] in [[Cambridge,
Massachusetts|Cambridge]], [[Massachusetts]], established in 1636. Its
history, influence and wealth have made it one of the most prestigious
universities in the world.{{cite book|title=Making Harvard Modern: The
Rise of America's
University|last1=Keller|first1=Morton|last2=Keller
|first2=Phyllis|publisher=Oxford University Press|isbn=0-19-514457-
0|quote=Harvard's professional schools... won world prestige of a sort
rarely seen among social institutions. (...) Harvard's age, wealth,
quality, and prestige may well shield it from any conceivable
vicissitudes.|year=2001|pages=463–481}}{{Cite book|title=How Harvard
Rules: Reason in the Service of Empire|quote=... [Harvard's] tremendous
institutional power and prestige (...) Within the nation's (arguably)
most prestigious institution of higher learning ...|chapter=Sexual
Shakedown|pages=326–336|year=1989|publisher=South End Press|isbn=0-
89608-284-9|editor1-first=John|last=Spaulding|first=Christina|editor-
last=Trumpbour}}{{cite web|url=http://www.bloomberg.com/news/2011-03-
10/harvard-mit-ranked-most-prestigious-universities-study-
reports.html|title=Harvard, MIT Ranked Most Prestigious Universities,
Study Reports|author=David Altaner|publisher=Bloomberg|date=March 9,
2011|accessdate=March 1, 2012}}{{cite book|title=Collier's
Encyclopedia|publisher=Macmillan Educational Co.|year=1986|quote=Harvard
University, one of the world's most prestigious institutions of higher
learning, was founded in Massachusetts in 1636.}}{{cite
web|last=Newport|first=Frank|title=Harvard Number One University in Eyes
of Public Stanford and Yale in second
place|url=http://www.gallup.com/poll/9109/harvard-number-one-university-
eyes-public.aspx|publisher=Gallup}} Established originally by the
[[Massachusetts General Court|Massachusetts legislature]] and soon
thereafter named for [[John Harvard (clergyman)|John Harvard]] (its first
benefactor), Harvard is the [[Colonial Colleges|United States' oldest
institution of higher learning]],{{cite book|first1=Frederick
|last1=Rudolph|title=The American College and
University|year=1961|page=3|isbn=0-8203-1285-1|publisher=University of
Georgia Press}} and the [[Harvard Corporation]] (formally, the
''President and Fellows of Harvard College'')';
$re = "/[^|]*\bpresident\b[^|]*/i";
if (preg_match_all($re, $a, $result)) {
var_dump($result)
}
?>
var_dump($result) 给出了 "author=Marvin Hightower" 的结果，但是我希望基于我的表达式的结果是：“|president = [[Drew Gilpin Faust]]”。我错过了什么？
(?:^|(?<=\|))[^|]*\bpresident\b[^|]*(?=\||$)
使用 this.See 演示。
https://regex101.com/r/sS2dM8/3
问题是因为松散的末端导致灾难性的 backtracking.Just 修复末端并且它有效 fine.The 正则表达式本身并没有错但是它在大数据上生成了太多的组合并且失败引用灾难性错误。
我有以下字符串 ($a) 并试图隔离从分隔符“|”开始的文本其中单词 "president" 直到下一个相同的分隔符“|”，我有以下代码，其中 returns 比预期更多的数据。
<?php
$a = '{{Redirect|Harvard}} {{pp-move-indef}} {{Use mdy dates|date=August
2014}} {{pp-semi-blp|small=yes}}{{Infobox university |name = Harvard
University |image_name = Harvard Wreath Logo 1.svg |image_size = |caption
= [[Seal (emblem)|Seal]] of Harvard University |latin_name = Universitas
Harvardiana |motto = ''Veritas''Harvard's ''Veritas'' appears on the
university's arms; [[Heraldry|heraldically]] speaking, however, a 'motto'
is a word or phrase displayed on a scroll in conjunction with a shield of
arms. [https://books.google.com/books?
id=zkQWZaZqZfUC&pg=PA330&lpg=PA330#v=onepage&q&f=false Since 1692]
University [[seal (device)|seals]] have borne ''Christo et Ecclesiae''
(for Christ and the Church) in this manner, arguably making that phrase
the university's motto in a heraldic sense. This legend is otherwise not
in general use today. |established = 1636An appropriation of £400 toward
a "school or college" was voted on October 28, 1636 (OS), at a meeting
which convened on September 8 and was adjourned to October 28. Some
sources consider October 28, 1636 (OS) (November 7, 1636 NS) to be the
date of founding. Harvard's 1936 tercentenary celebration treated
September 18 as the founding date, though 1836 bicentennial was
celebrated on September 8, 1836. Sources: meeting dates, {{cite
book|first=Josiah|last=Quincy|title=History of Harvard University
|year=1860 |publisher=Crosby, Nichols, Lee and Co.|location=117
Washington Street, Boston}}, [https://books.google.com/books?
vid=OCLC11636583&id=KynqxH_4lGUC&pg=RA1-PA586&lpg=RA1-PA586 p. 586], "At
a Court holden September 8th, 1636 and continued by adjournment to the
28th of the 8th month (October, 1636)... the Court agreed to give £400
towards a School or College, whereof £200 to be paid next year...."
Tercentenary dates: {{cite
news|url=http://www.time.com/time/
magazine/printout/0,8816,756722,00.html|date=September 28,
1936|accessdate=September 8, 2006|work=Time|title=Cambridge Birthday}}:
"Harvard claims birth on the day the Massachusetts Great and General
Court convened to authorize its founding. This was Sept. 8, 1637 under
the Julian calendar. Allowing for the ten-day advance of the Gregorian
calendar, Tercentenary officials arrived at Sept. 18 as the date for the
third and last big Day of the celebration;" "on Oct. 28, 1636 ... £400
for that 'school or college' [was voted by] the Great and General Court
of the [[Massachusetts Bay Colony]]." Bicentennial date: {{cite web
|url=http://www.news.harvard.edu/gazette/2003/10.02/02-
history.html|publisher=Harvard University|title=Harvard Gazette: This
Month in Harvard History|date=September 2, 2003 |accessdate=September 15,
2006|author=Marvin Hightower}}, "Sept. 8, 1836 - Some 1,100 to 1,300
alumni flock to Harvard's Bicentennial, at which a professional choir
premieres "Fair Harvard." ... guest speaker Josiah Quincy Jr., Class of
1821, makes a motion, unanimously adopted, 'that this assembly of the
Alumni be adjourned to meet at this place on September 8, 1936.'"
Tercentary opening of Quincy's sealed package: ''The New York Times,''
September 9, 1936, p. 24, "Package Sealed in 1836 Opened at Harvard. It
Held Letters Written at Bicentenary": "September 8th, 1936: As the first
formal function in the celebration of Harvard's tercentenary, the Harvard
Alumni Association witnessed the opening by President Conant of the
'mysterious' package sealed by President Josiah Quincy at the Harvard
bicentennial in 1836." |mottoeng = Truth |type = [[Private
university|Private]] – [[Research]] |calendar = Semester |endowment =
.4 billion{{As of|2014|06|30}}. {{cite web | title = Harvard Endowment
Earns 15.4% Return for Fiscal 2014| work = The Wall Street Journal | url
= http://online.wsj.com/articles/harvard-endowment-earns-15-4-return-for-
fiscal-2014-1411506002 | accessdate=10 October 2014}} |president = [[Drew
Gilpin Faust]] |students = 21,000{{As of|2014|09|01}}. {{cite web | title
= Harvard at a Glance| work = Harvard University | url =
http://www.harvard.edu/harvard-glance | accessdate=27 November 2014}}
|undergrad = 6,700 |postgrad = 14,500 |staff = |faculty = 4,671{{Cite
book|last=Office of Institutional Research.|title=Harvard University Fact
Book|year=2009|chapter=Faculty|url=http://
www.provost.harvard.edu/institutional_research/Provost_-_09_18-
19facuni.pdf}} ("Unduplicated, Paid Instructional Faculty Count: 2,107.
Unduplicated instructional faculty count is the most appropriate count
for general reporting purposes.") |city = [[Cambridge,
Massachusetts|Cambridge]] |state = [[Massachusetts]] |country = United
States |campus = [[Urban area|Urban]]{{Convert|210|acre|ha}} (Main
campus){{Convert|21|acre|ha}} (Medical campus)
{{Convert|360|acre|ha}} (Allston campus)
{{Convert|4500|acre|ha}} (other holdings) |sports = 42 varsity teams
|athletics = [[National Collegiate Athletic Association|NCAA]] [[Division
I (NCAA)|Division I]] – [[Ivy League]] |nickname = [[Harvard Crimson]]
|colors = {{color box|#A41034}} [[Crimson]]{{cite web|title=Color -
Identity Guidelines - Harvard Business
School|url=http://www.hbs.edu/marketing/color.html|publisher=Harvard
Business School|accessdate=26 September 2014}} |free_label = Student
newspaper |free = ''[[The Harvard Crimson]]'' |affiliations = [[National
Association of Independent Colleges and Universities|NAICU]]
[[Association of Independent Colleges and Universities in
Massachusetts|AICUM]][[Association of American Universities|AAU]]
[[Universities Research Association|URA]] |website =
{{URL|http://www.harvard.edu/|Harvard.edu}} |logo = [[File:Harvard
University logo.PNG|Harvard University logo (with its coat of arms)]]
|publictransit = [[Harvard (MBTA station)]] }} '''Harvard University'''
is a [[Private university|private]] [[Ivy League]] [[Doctoral
university|research university]] in [[Cambridge,
Massachusetts|Cambridge]], [[Massachusetts]], established in 1636. Its
history, influence and wealth have made it one of the most prestigious
universities in the world.{{cite book|title=Making Harvard Modern: The
Rise of America's
University|last1=Keller|first1=Morton|last2=Keller
|first2=Phyllis|publisher=Oxford University Press|isbn=0-19-514457-
0|quote=Harvard's professional schools... won world prestige of a sort
rarely seen among social institutions. (...) Harvard's age, wealth,
quality, and prestige may well shield it from any conceivable
vicissitudes.|year=2001|pages=463–481}}{{Cite book|title=How Harvard
Rules: Reason in the Service of Empire|quote=... [Harvard's] tremendous
institutional power and prestige (...) Within the nation's (arguably)
most prestigious institution of higher learning ...|chapter=Sexual
Shakedown|pages=326–336|year=1989|publisher=South End Press|isbn=0-
89608-284-9|editor1-first=John|last=Spaulding|first=Christina|editor-
last=Trumpbour}}{{cite web|url=http://www.bloomberg.com/news/2011-03-
10/harvard-mit-ranked-most-prestigious-universities-study-
reports.html|title=Harvard, MIT Ranked Most Prestigious Universities,
Study Reports|author=David Altaner|publisher=Bloomberg|date=March 9,
2011|accessdate=March 1, 2012}}{{cite book|title=Collier's
Encyclopedia|publisher=Macmillan Educational Co.|year=1986|quote=Harvard
University, one of the world's most prestigious institutions of higher
learning, was founded in Massachusetts in 1636.}}{{cite
web|last=Newport|first=Frank|title=Harvard Number One University in Eyes
of Public Stanford and Yale in second
place|url=http://www.gallup.com/poll/9109/harvard-number-one-university-
eyes-public.aspx|publisher=Gallup}} Established originally by the
[[Massachusetts General Court|Massachusetts legislature]] and soon
thereafter named for [[John Harvard (clergyman)|John Harvard]] (its first
benefactor), Harvard is the [[Colonial Colleges|United States' oldest
institution of higher learning]],{{cite book|first1=Frederick
|last1=Rudolph|title=The American College and
University|year=1961|page=3|isbn=0-8203-1285-1|publisher=University of
Georgia Press}} and the [[Harvard Corporation]] (formally, the
''President and Fellows of Harvard College'')';
$re = "/[^|]*\bpresident\b[^|]*/i";
if (preg_match_all($re, $a, $result)) {
var_dump($result)
}
?>
var_dump($result) 给出了 "author=Marvin Hightower" 的结果，但是我希望基于我的表达式的结果是：“|president = [[Drew Gilpin Faust]]”。我错过了什么？
(?:^|(?<=\|))[^|]*\bpresident\b[^|]*(?=\||$)
使用 this.See 演示。
https://regex101.com/r/sS2dM8/3
问题是因为松散的末端导致灾难性的 backtracking.Just 修复末端并且它有效 fine.The 正则表达式本身并没有错但是它在大数据上生成了太多的组合并且失败引用灾难性错误。