/the quick brown fox/

    the quick brown fox

    The quick brown FOX

    What do you know about the quick brown fox?

    What do you know about THE QUICK BROWN FOX?

/The quick brown fox/i

    the quick brown fox

    The quick brown FOX

    What do you know about the quick brown fox?

    What do you know about THE QUICK BROWN FOX?

/abcd\t\n\r\f\a\e\071\x3b\$\\\?caxyz/

    abcd\t\n\r\f\a\e9;\$\\?caxyz

/a*abc?xyz+pqr{3}ab{2,}xy{4,5}pq{0,6}AB{0,}zz/

    abxyzpqrrrabbxyyyypqAzz

    abxyzpqrrrabbxyyyypqAzz

    aabxyzpqrrrabbxyyyypqAzz

    aaabxyzpqrrrabbxyyyypqAzz

    aaaabxyzpqrrrabbxyyyypqAzz

    abcxyzpqrrrabbxyyyypqAzz

    aabcxyzpqrrrabbxyyyypqAzz

    aaabcxyzpqrrrabbxyyyypAzz

    aaabcxyzpqrrrabbxyyyypqAzz

    aaabcxyzpqrrrabbxyyyypqqAzz

    aaabcxyzpqrrrabbxyyyypqqqAzz

    aaabcxyzpqrrrabbxyyyypqqqqAzz

    aaabcxyzpqrrrabbxyyyypqqqqqAzz

    aaabcxyzpqrrrabbxyyyypqqqqqqAzz

    aaaabcxyzpqrrrabbxyyyypqAzz

    abxyzzpqrrrabbxyyyypqAzz

    aabxyzzzpqrrrabbxyyyypqAzz

    aaabxyzzzzpqrrrabbxyyyypqAzz

    aaaabxyzzzzpqrrrabbxyyyypqAzz

    abcxyzzpqrrrabbxyyyypqAzz

    aabcxyzzzpqrrrabbxyyyypqAzz

    aaabcxyzzzzpqrrrabbxyyyypqAzz

    aaaabcxyzzzzpqrrrabbxyyyypqAzz

    aaaabcxyzzzzpqrrrabbbxyyyypqAzz

    aaaabcxyzzzzpqrrrabbbxyyyyypqAzz

    aaabcxyzpqrrrabbxyyyypABzz

    aaabcxyzpqrrrabbxyyyypABBzz

    >>>aaabxyzpqrrrabbxyyyypqAzz

    >aaaabxyzpqrrrabbxyyyypqAzz

    >>>>abcxyzpqrrrabbxyyyypqAzz

    *** Failers

    abxyzpqrrabbxyyyypqAzz

    abxyzpqrrrrabbxyyyypqAzz

    abxyzpqrrrabxyyyypqAzz

    aaaabcxyzzzzpqrrrabbbxyyyyyypqAzz

    aaaabcxyzzzzpqrrrabbbxyyypqAzz

    aaabcxyzpqrrrabbxyyyypqqqqqqqAzz

/^(abc){1,2}zz/

    abczz

    abcabczz

    *** Failers

    zz

    abcabcabczz

    >>abczz

/^(b+?|a){1,2}?c/

    bc

    bbc

    bbbc

    bac

    bbac

    aac

    abbbbbbbbbbbc

    bbbbbbbbbbbac

    *** Failers

    aaac

    abbbbbbbbbbbac

/^(b+|a){1,2}c/

    bc

    bbc

    bbbc

    bac

    bbac

    aac

    abbbbbbbbbbbc

    bbbbbbbbbbbac

    *** Failers

    aaac

    abbbbbbbbbbbac

/^(b+|a){1,2}?bc/

    bbc

/^(b*|ba){1,2}?bc/

    babc

    bbabc

    bababc

    *** Failers

    bababbc

    babababc

/^(ba|b*){1,2}?bc/

    babc

    bbabc

    bababc

    *** Failers

    bababbc

    babababc

/^\ca\cA\c[\c{\c:/

    \x01\x01\e;z

/^[ab\]cde]/

    athing

    bthing

    ]thing

    cthing

    dthing

    ething

    *** Failers

    fthing

    [thing

    \\thing

/^[]cde]/

    ]thing

    cthing

    dthing

    ething

    *** Failers

    athing

    fthing

/^[^ab\]cde]/

    fthing

    [thing

    \\thing

    *** Failers

    athing

    bthing

    ]thing

    cthing

    dthing

    ething

/^[^]cde]/

    athing

    fthing

    *** Failers

    ]thing

    cthing

    dthing

    ething

/^\�/

    �

/^ÿ/

    ÿ

/^[0-9]+$/

    0

    1

    2

    3

    4

    5

    6

    7

    8

    9

    10

    100

    *** Failers

    abc

/^.*nter/

    enter

    inter

    uponter

/^xxx[0-9]+$/

    xxx0

    xxx1234

    *** Failers

    xxx

/^.+[0-9][0-9][0-9]$/

    x123

    xx123

    123456

    *** Failers

    123

    x1234

/^.+?[0-9][0-9][0-9]$/

    x123

    xx123

    123456

    *** Failers

    123

    x1234

/^([^!]+)!(.+)=apquxz\.ixr\.zzz\.ac\.uk$/

    abc!pqr=apquxz.ixr.zzz.ac.uk

    *** Failers

    !pqr=apquxz.ixr.zzz.ac.uk

    abc!=apquxz.ixr.zzz.ac.uk

    abc!pqr=apquxz:ixr.zzz.ac.uk

    abc!pqr=apquxz.ixr.zzz.ac.ukk

/:/

    Well, we need a colon: somewhere

    *** Fail if we don't

/([\da-f:]+)$/i

    0abc

    abc

    fed

    E

    ::

    5f03:12C0::932e

    fed def

    Any old stuff

    *** Failers

    0zzz

    gzzz

    fed\x20

    Any old rubbish

/^.*\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/

    .1.2.3

    A.12.123.0

    *** Failers

    .1.2.3333

    1.2.3

    1234.2.3

/^(\d+)\s+IN\s+SOA\s+(\S+)\s+(\S+)\s*\(\s*$/

    1 IN SOA non-sp1 non-sp2(

    1    IN    SOA    non-sp1    non-sp2   (

    *** Failers

    1IN SOA non-sp1 non-sp2(

/^[a-zA-Z\d][a-zA-Z\d\-]*(\.[a-zA-Z\d][a-zA-z\d\-]*)*\.$/

    a.

    Z.

    2.

    ab-c.pq-r.

    sxk.zzz.ac.uk.

    x-.y-.

    *** Failers

    -abc.peq.

/^\*\.[a-z]([a-z\-\d]*[a-z\d]+)?(\.[a-z]([a-z\-\d]*[a-z\d]+)?)*$/

    *.a

    *.b0-a

    *.c3-b.c

    *.c-a.b-c

    *** Failers

    *.0

    *.a-

    *.a-b.c-

    *.c-a.0-c

/^(?=ab(de))(abd)(e)/

    abde

/^(?!(ab)de|x)(abd)(f)/

    abdf

/^(?=(ab(cd)))(ab)/

    abcd

/^[\da-f](\.[\da-f])*$/i

    a.b.c.d

    A.B.C.D

    a.b.c.1.2.3.C

/^\".*\"\s*(;.*)?$/

    \"1234\"

    \"abcd\" ;

    \"\" ; rhubarb

    *** Failers

    \"1234\" : things

/^$/

    \

    *** Failers

/   ^    a   (?# begins with a)  b\sc (?# then b c) $ (?# then end)/x

    ab c

    *** Failers

    abc

    ab cde

/(?x)   ^    a   (?# begins with a)  b\sc (?# then b c) $ (?# then end)/

    ab c

    *** Failers

    abc

    ab cde

/^   a\ b[c ]d       $/x

    a bcd

    a b d

    *** Failers

    abcd

    ab d

/^(a(b(c)))(d(e(f)))(h(i(j)))(k(l(m)))$/

    abcdefhijklm

/^(?:a(b(c)))(?:d(e(f)))(?:h(i(j)))(?:k(l(m)))$/

    abcdefhijklm

/^[\w][\W][\s][\S][\d][\D][\b][\n][\c]][\022]/

    a+ Z0+\x08\n\x1d\x12

/^[.^$|()*+?{,}]+/

    .^\$(*+)|{?,?}

/^a*\w/

    z

    az

    aaaz

    a

    aa

    aaaa

    a+

    aa+

/^a*?\w/

    z

    az

    aaaz

    a

    aa

    aaaa

    a+

    aa+

/^a+\w/

    az

    aaaz

    aa

    aaaa

    aa+

/^a+?\w/

    az

    aaaz

    aa

    aaaa

    aa+

/^\d{8}\w{2,}/

    1234567890

    12345678ab

    12345678__

    *** Failers

    1234567

/^[aeiou\d]{4,5}$/

    uoie

    1234

    12345

    aaaaa

    *** Failers

    123456

/^[aeiou\d]{4,5}?/

    uoie

    1234

    12345

    aaaaa

    123456

/\A(abc|def)=(\1){2,3}\Z/

    abc=abcabc

    def=defdefdef

    *** Failers

    abc=defdef

/^(a)(b)(c)(d)(e)(f)(g)(h)(i)(j)(k)\11*(\3\4)\1(?#)2$/

    abcdefghijkcda2

    abcdefghijkkkkcda2

/(cat(a(ract|tonic)|erpillar)) \1()2(3)/

    cataract cataract23

    catatonic catatonic23

    caterpillar caterpillar23

/^From +([^ ]+) +[a-zA-Z][a-zA-Z][a-zA-Z] +[a-zA-Z][a-zA-Z][a-zA-Z] +[0-9]?[0-9] +[0-9][0-9]:[0-9][0-9]/

    From abcd  Mon Sep 01 12:33:02 1997

/^From\s+\S+\s+([a-zA-Z]{3}\s+){2}\d{1,2}\s+\d\d:\d\d/

    From abcd  Mon Sep 01 12:33:02 1997

    From abcd  Mon Sep  1 12:33:02 1997

    *** Failers

    From abcd  Sep 01 12:33:02 1997

/^12.34/s

    12\n34

    12\r34

/\w+(?=\t)/

    the quick brown\t fox

/foo(?!bar)(.*)/

    foobar is foolish see?

/(?:(?!foo)...|^.{0,2})bar(.*)/

    foobar crowbar etc

    barrel

    2barrel

    A barrel

/^(\D*)(?=\d)(?!123)/

    abc456

    *** Failers

    abc123

/^1234(?# test newlines

  inside)/

    1234

/^1234 #comment in extended re

  /x

    1234

/#rhubarb

  abcd/x

    abcd

/^abcd#rhubarb/x

    abcd

/^(a)\1{2,3}(.)/

    aaab

    aaaab

    aaaaab

    aaaaaab

/(?!^)abc/

    the abc

    *** Failers

    abc

/(?=^)abc/

    abc

    *** Failers

    the abc

/^[ab]{1,3}(ab*|b)/

    aabbbbb

/^[ab]{1,3}?(ab*|b)/

    aabbbbb

/^[ab]{1,3}?(ab*?|b)/

    aabbbbb

/^[ab]{1,3}(ab*?|b)/

    aabbbbb

/  (?: [\040\t] |  \(

(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*

\)  )*                          # optional leading comment

(?:    (?:

[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...

(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom

|

" (?:                      # opening quote...

[^\\\x80-\xff\n\015"]                #   Anything except backslash and quote

|                     #    or

\\ [^\x80-\xff]           #   Escaped something (something != CR)

)* "  # closing quote

)                    # initial word

(?:  (?: [\040\t] |  \(

(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*

\)  )*  \.  (?: [\040\t] |  \(

(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*

\)  )*   (?:

[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...

(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom

|

" (?:                      # opening quote...

[^\\\x80-\xff\n\015"]                #   Anything except backslash and quote

|                     #    or

\\ [^\x80-\xff]           #   Escaped something (something != CR)

)* "  # closing quote

)  )* # further okay, if led by a period

(?: [\040\t] |  \(

(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*

\)  )*  @  (?: [\040\t] |  \(

(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*

\)  )*    (?:

[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...

(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom

|   \[                         # [

(?: [^\\\x80-\xff\n\015\[\]] |  \\ [^\x80-\xff]  )*    #    stuff

\]                        #           ]

)                           # initial subdomain

(?:                                  #

(?: [\040\t] |  \(

(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*

\)  )*  \.                        # if led by a period...

(?: [\040\t] |  \(

(?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  |  \( (?:  [^\\\x80-\xff\n\015()]  |  \\ [^\x80-\xff]  )* \)  )*

\)  )*   (?:

[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...

(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom

|   \[                         # [

(?: [^\\\x80-\xff\n\015\[\]] |  \\ [^\x80-\xff]  )*    #    stuff

\]                        #           ]

)                     #   ...further okay

)*

# address

|                     #  or

(?:

[^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]+    # some number of atom characters...

(?![^(\040)<>@,;:".\\\[\]\000-\037\x80-\xff]) # ..not followed by something that could be part of an atom

|

" (?:                      # opening quote...

[^\\\x80-\xff\n\015"]                #   Anything except backslash and quote

|                     #    or

\\ [^\x80-\xff]           #   Escaped something (something != CR)

)* "  # closing quote

)             # one word, optionally followed by....