/(a)b|/I

Capturing subpattern count = 1

No options

No first char

No need char

/abc/I

Capturing subpattern count = 0

No options

First char = 'a'

Need char = 'c'

    abc

 0: abc

    defabc

 0: abc

    \Aabc

 0: abc

    *** Failers

No match

    \Adefabc

No match

    ABC

No match

/^abc/I

Capturing subpattern count = 0

Options: anchored

No first char

No need char

    abc

 0: abc

    \Aabc

 0: abc

    *** Failers

No match

    defabc

No match

    \Adefabc

No match

/a+bc/I

Capturing subpattern count = 0

Partial matching not supported

No options

First char = 'a'

Need char = 'c'

/a*bc/I

Capturing subpattern count = 0

Partial matching not supported

No options

No first char

Need char = 'c'

/a{3}bc/I

Capturing subpattern count = 0

Partial matching not supported

No options

First char = 'a'

Need char = 'c'

/(abc|a+z)/I

Capturing subpattern count = 1

Partial matching not supported

No options

First char = 'a'

No need char

/^abc$/I

Capturing subpattern count = 0

Options: anchored

No first char

No need char

    abc

 0: abc

    *** Failers

No match

    def\nabc

No match

/ab\idef/X

Failed: unrecognized character follows \ at offset 3

/(?X)ab\idef/X

Failed: unrecognized character follows \ at offset 7

/x{5,4}/

Failed: numbers out of order in {} quantifier at offset 5

/z{65536}/

Failed: number too big in {} quantifier at offset 7

/[abcd/

Failed: missing terminating ] for character class at offset 5

/(?X)[\B]/

Failed: invalid escape sequence in character class at offset 6

/[z-a]/

Failed: range out of order in character class at offset 3

/^*/

Failed: nothing to repeat at offset 1

/(abc/

Failed: missing ) at offset 4

/(?# abc/

Failed: missing ) after comment at offset 7

/(?z)abc/

Failed: unrecognized character after (? or (?- at offset 2

/.*b/I

Capturing subpattern count = 0

Partial matching not supported

No options

First char at start or follows newline

Need char = 'b'

/.*?b/I

Capturing subpattern count = 0

Partial matching not supported

No options

First char at start or follows newline

Need char = 'b'

/cat|dog|elephant/I

Capturing subpattern count = 0

No options

No first char

No need char

    this sentence eventually mentions a cat

 0: cat

    this sentences rambles on and on for a while and then reaches elephant

 0: elephant

/cat|dog|elephant/IS

Capturing subpattern count = 0

No options

No first char

No need char

Starting byte set: c d e 

    this sentence eventually mentions a cat

 0: cat

    this sentences rambles on and on for a while and then reaches elephant

 0: elephant

/cat|dog|elephant/IiS

Capturing subpattern count = 0

Options: caseless

No first char

No need char

Starting byte set: C D E c d e 

    this sentence eventually mentions a CAT cat

 0: CAT

    this sentences rambles on and on for a while to elephant ElePhant

 0: elephant

/a|[bcd]/IS

Capturing subpattern count = 0

No options

No first char

No need char

Starting byte set: a b c d 

/(a|[^\dZ])/IS

Capturing subpattern count = 1

No options

No first char

No need char

Starting byte set: \x00 \x01 \x02 \x03 \x04 \x05 \x06 \x07 \x08 \x09 \x0a 

  \x0b \x0c \x0d \x0e \x0f \x10 \x11 \x12 \x13 \x14 \x15 \x16 \x17 \x18 \x19 

  \x1a \x1b \x1c \x1d \x1e \x1f \x20 ! " # $ % & ' ( ) * + , - . / : ; < = > 

  ? @ A B C D E F G H I J K L M N O P Q R S T U V W X Y [ \ ] ^ _ ` a b c d 

  e f g h i j k l m n o p q r s t u v w x y z { | } ~ \x7f \x80 \x81 \x82 \x83 

  \x84 \x85 \x86 \x87 \x88 \x89 \x8a \x8b \x8c \x8d \x8e \x8f \x90 \x91 \x92 

  \x93 \x94 \x95 \x96 \x97 \x98 \x99 \x9a \x9b \x9c \x9d \x9e \x9f \xa0 \xa1 

  \xa2 \xa3 \xa4 \xa5 \xa6 \xa7 \xa8 \xa9 \xaa \xab \xac \xad \xae \xaf \xb0 

  \xb1 \xb2 \xb3 \xb4 \xb5 \xb6 \xb7 \xb8 \xb9 \xba \xbb \xbc \xbd \xbe \xbf 

  \xc0 \xc1 \xc2 \xc3 \xc4 \xc5 \xc6 \xc7 \xc8 \xc9 \xca \xcb \xcc \xcd \xce 

  \xcf \xd0 \xd1 \xd2 \xd3 \xd4 \xd5 \xd6 \xd7 \xd8 \xd9 \xda \xdb \xdc \xdd 

  \xde \xdf \xe0 \xe1 \xe2 \xe3 \xe4 \xe5 \xe6 \xe7 \xe8 \xe9 \xea \xeb \xec 

  \xed \xee \xef \xf0 \xf1 \xf2 \xf3 \xf4 \xf5 \xf6 \xf7 \xf8 \xf9 \xfa \xfb 

  \xfc \xfd \xfe \xff 

/(a|b)*[\s]/IS

Capturing subpattern count = 1

No options

No first char

No need char

Starting byte set: \x09 \x0a \x0c \x0d \x20 a b 

/(ab\2)/

Failed: reference to non-existent subpattern at offset 6

/{4,5}abc/

Failed: nothing to repeat at offset 4

/(a)(b)(c)\2/I

Capturing subpattern count = 3

Max back reference = 2

No options

First char = 'a'

Need char = 'c'

    abcb

 0: abcb

 1: a

 2: b

 3: c

    \O0abcb

Matched, but too many substrings

    \O3abcb

Matched, but too many substrings

 0: abcb

    \O6abcb

Matched, but too many substrings

 0: abcb

 1: a

    \O9abcb

Matched, but too many substrings

 0: abcb

 1: a

 2: b

    \O12abcb

 0: abcb

 1: a

 2: b

 3: c

/(a)bc|(a)(b)\2/I

Capturing subpattern count = 3

Max back reference = 2

No options

First char = 'a'

No need char

    abc

 0: abc

 1: a

    \O0abc

Matched, but too many substrings

    \O3abc

Matched, but too many substrings

 0: abc

    \O6abc

 0: abc

 1: a

    aba

 0: aba

 1: <unset>

 2: a

 3: b

    \O0aba

Matched, but too many substrings

    \O3aba

Matched, but too many substrings

 0: aba

    \O6aba

Matched, but too many substrings

 0: aba

 1: <unset>

    \O9aba

Matched, but too many substrings

 0: aba

 1: <unset>

 2: a

    \O12aba

 0: aba

 1: <unset>

 2: a

 3: b

/abc$/IE

Capturing subpattern count = 0

Options: dollar_endonly

First char = 'a'

Need char = 'c'

    abc

 0: abc

    *** Failers

No match

    abc\n

No match

    abc\ndef

No match

/(a)(b)(c)(d)(e)\6/

Failed: reference to non-existent subpattern at offset 17

/the quick brown fox/I

Capturing subpattern count = 0

No options

First char = 't'

Need char = 'x'

    the quick brown fox

 0: the quick brown fox

    this is a line with the quick brown fox

 0: the quick brown fox

/the quick brown fox/IA

Capturing subpattern count = 0

Options: anchored

No first char

No need char

    the quick brown fox

 0: the quick brown fox

    *** Failers

No match

    this is a line with the quick brown fox

No match

/ab(?z)cd/

Failed: unrecognized character after (? or (?- at offset 4

/^abc|def/I

Capturing subpattern count = 0

No options

No first char

No need char

    abcdef

 0: abc

    abcdef\B

 0: def

/.*((abc)$|(def))/I

Capturing subpattern count = 3

Partial matching not supported

No options

First char at start or follows newline

No need char

    defabc

 0: defabc

 1: abc

 2: abc

    \Zdefabc

 0: def

 1: def

 2: <unset>

 3: def

/abc/IP

    abc

 0: abc

    *** Failers

No match: POSIX code 17: match failed

/^abc|def/IP

    abcdef

 0: abc

    abcdef\B

 0: def

/.*((abc)$|(def))/IP

    defabc

 0: defabc

 1: abc

 2: abc

    \Zdefabc

 0: def

 1: def

 3: def

/the quick brown fox/IP

    the quick brown fox

 0: the quick brown fox

    *** Failers

No match: POSIX code 17: match failed

    The Quick Brown Fox

No match: POSIX code 17: match failed

/the quick brown fox/IPi

    the quick brown fox

 0: the quick brown fox

    The Quick Brown Fox

 0: The Quick Brown Fox

/abc.def/IP

    *** Failers

No match: POSIX code 17: match failed

    abc\ndef

No match: POSIX code 17: match failed

/abc$/IP

    abc

 0: abc

    abc\n

 0: abc

/(abc)\2/IP

Failed: POSIX code 15: bad back reference at offset 7     

/(abc\1)/IP

    abc

No match: POSIX code 17: match failed

/)/

Failed: unmatched parentheses at offset 0

/a[]b/

Failed: missing terminating ] for character class at offset 4

/[^aeiou ]{3,}/I

Capturing subpattern count = 0

Partial matching not supported

No options

No first char

No need char

    co-processors, and for

 0: -pr

/<.*>/I

Capturing subpattern count = 0

Partial matching not supported

No options

First char = '<'

Need char = '>'

    abc<def>ghi<klm>nop

 0: <def>ghi<klm>

/<.*?>/I

Capturing subpattern count = 0

Partial matching not supported

No options

First char = '<'

Need char = '>'

    abc<def>ghi<klm>nop

 0: <def>

/<.*>/IU

Capturing subpattern count = 0

Partial matching not supported

Options: ungreedy

First char = '<'

Need char = '>'

    abc<def>ghi<klm>nop

 0: <def>

/(?U)<.*>/I

Capturing subpattern count = 0

Partial matching not supported

Options: ungreedy

First char = '<'

Need char = '>'

    abc<def>ghi<klm>nop

 0: <def>

/<.*?>/IU

Capturing subpattern count = 0

Partial matching not supported

Options: ungreedy

First char = '<'

Need char = '>'

    abc<def>ghi<klm>nop

 0: <def>ghi<klm>

/={3,}/IU

Capturing subpattern count = 0

Partial matching not supported

Options: ungreedy

First char = '='

Need char = '='

    abc========def

 0: ===

/(?U)={3,}?/I

Capturing subpattern count = 0

Partial matching not supported

Options: ungreedy

First char = '='

Need char = '='

    abc========def

 0: ========

/(?<!bar|cattle)foo/I

Capturing subpattern count = 0

No options

First char = 'f'

Need char = 'o'

    foo

 0: foo

    catfoo

 0: foo

    *** Failers

No match

    the barfoo

No match

    and cattlefoo

No match

/(?<=a+)b/

Failed: lookbehind assertion is not fixed length at offset 6

/(?<=aaa|b{0,3})b/

Failed: lookbehind assertion is not fixed length at offset 14

/(?<!(foo)a\1)bar/

Failed: lookbehind assertion is not fixed length at offset 12

/(?i)abc/I

Capturing subpattern count = 0

Options: caseless

First char = 'a' (caseless)

Need char = 'c' (caseless)

/(a|(?m)a)/I

Capturing subpattern count = 1

No options

First char = 'a'

No need char

/(?i)^1234/I

Capturing subpattern count = 0

Options: anchored caseless

No first char

No need char

/(^b|(?i)^d)/I

Capturing subpattern count = 1

Options: anchored

No first char

No need char

/(?s).*/I

Capturing subpattern count = 0

Partial matching not supported

Options: anchored dotall

No first char

No need char