1 | =head1 NAME
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2 |
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3 | perlreref - Perl Regular Expressions Reference
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4 |
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5 | =head1 DESCRIPTION
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6 |
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7 | This is a quick reference to Perl's regular expressions.
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8 | For full information see L<perlre> and L<perlop>, as well
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9 | as the L</"SEE ALSO"> section in this document.
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10 |
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11 | =head2 OPERATORS
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12 |
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13 | =~ determines to which variable the regex is applied.
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14 | In its absence, $_ is used.
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15 |
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16 | $var =~ /foo/;
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17 |
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18 | !~ determines to which variable the regex is applied,
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19 | and negates the result of the match; it returns
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20 | false if the match succeeds, and true if it fails.
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21 |
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22 | $var !~ /foo/;
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23 |
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24 | m/pattern/igmsoxc searches a string for a pattern match,
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25 | applying the given options.
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26 |
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27 | i case-Insensitive
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28 | g Global - all occurrences
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29 | m Multiline mode - ^ and $ match internal lines
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30 | s match as a Single line - . matches \n
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31 | o compile pattern Once
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32 | x eXtended legibility - free whitespace and comments
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33 | c don't reset pos on failed matches when using /g
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34 |
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35 | If 'pattern' is an empty string, the last I<successfully> matched
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36 | regex is used. Delimiters other than '/' may be used for both this
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37 | operator and the following ones.
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38 |
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39 | qr/pattern/imsox lets you store a regex in a variable,
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40 | or pass one around. Modifiers as for m// and are stored
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41 | within the regex.
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42 |
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43 | s/pattern/replacement/igmsoxe substitutes matches of
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44 | 'pattern' with 'replacement'. Modifiers as for m//
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45 | with one addition:
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46 |
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47 | e Evaluate replacement as an expression
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48 |
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49 | 'e' may be specified multiple times. 'replacement' is interpreted
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50 | as a double quoted string unless a single-quote (') is the delimiter.
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51 |
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52 | ?pattern? is like m/pattern/ but matches only once. No alternate
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53 | delimiters can be used. Must be reset with L<reset|perlfunc/reset>.
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54 |
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55 | =head2 SYNTAX
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56 |
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57 | \ Escapes the character immediately following it
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58 | . Matches any single character except a newline (unless /s is used)
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59 | ^ Matches at the beginning of the string (or line, if /m is used)
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60 | $ Matches at the end of the string (or line, if /m is used)
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61 | * Matches the preceding element 0 or more times
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62 | + Matches the preceding element 1 or more times
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63 | ? Matches the preceding element 0 or 1 times
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64 | {...} Specifies a range of occurrences for the element preceding it
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65 | [...] Matches any one of the characters contained within the brackets
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66 | (...) Groups subexpressions for capturing to $1, $2...
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67 | (?:...) Groups subexpressions without capturing (cluster)
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68 | | Matches either the subexpression preceding or following it
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69 | \1, \2 ... The text from the Nth group
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70 |
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71 | =head2 ESCAPE SEQUENCES
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72 |
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73 | These work as in normal strings.
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74 |
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75 | \a Alarm (beep)
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76 | \e Escape
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77 | \f Formfeed
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78 | \n Newline
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79 | \r Carriage return
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80 | \t Tab
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81 | \037 Any octal ASCII value
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82 | \x7f Any hexadecimal ASCII value
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83 | \x{263a} A wide hexadecimal value
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84 | \cx Control-x
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85 | \N{name} A named character
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86 |
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87 | \l Lowercase next character
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88 | \u Titlecase next character
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89 | \L Lowercase until \E
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90 | \U Uppercase until \E
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91 | \Q Disable pattern metacharacters until \E
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92 | \E End case modification
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93 |
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94 | For Titlecase, see L</Titlecase>.
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95 |
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96 | This one works differently from normal strings:
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97 |
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98 | \b An assertion, not backspace, except in a character class
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99 |
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100 | =head2 CHARACTER CLASSES
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101 |
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102 | [amy] Match 'a', 'm' or 'y'
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103 | [f-j] Dash specifies "range"
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104 | [f-j-] Dash escaped or at start or end means 'dash'
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105 | [^f-j] Caret indicates "match any character _except_ these"
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106 |
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107 | The following sequences work within or without a character class.
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108 | The first six are locale aware, all are Unicode aware. The default
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109 | character class equivalent are given. See L<perllocale> and
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110 | L<perlunicode> for details.
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111 |
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112 | \d A digit [0-9]
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113 | \D A nondigit [^0-9]
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114 | \w A word character [a-zA-Z0-9_]
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115 | \W A non-word character [^a-zA-Z0-9_]
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116 | \s A whitespace character [ \t\n\r\f]
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117 | \S A non-whitespace character [^ \t\n\r\f]
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118 |
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119 | \C Match a byte (with Unicode, '.' matches a character)
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120 | \pP Match P-named (Unicode) property
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121 | \p{...} Match Unicode property with long name
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122 | \PP Match non-P
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123 | \P{...} Match lack of Unicode property with long name
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124 | \X Match extended unicode sequence
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125 |
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126 | POSIX character classes and their Unicode and Perl equivalents:
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127 |
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128 | alnum IsAlnum Alphanumeric
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129 | alpha IsAlpha Alphabetic
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130 | ascii IsASCII Any ASCII char
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131 | blank IsSpace [ \t] Horizontal whitespace (GNU extension)
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132 | cntrl IsCntrl Control characters
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133 | digit IsDigit \d Digits
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134 | graph IsGraph Alphanumeric and punctuation
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135 | lower IsLower Lowercase chars (locale and Unicode aware)
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136 | print IsPrint Alphanumeric, punct, and space
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137 | punct IsPunct Punctuation
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138 | space IsSpace [\s\ck] Whitespace
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139 | IsSpacePerl \s Perl's whitespace definition
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140 | upper IsUpper Uppercase chars (locale and Unicode aware)
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141 | word IsWord \w Alphanumeric plus _ (Perl extension)
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142 | xdigit IsXDigit [0-9A-Fa-f] Hexadecimal digit
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143 |
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144 | Within a character class:
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145 |
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146 | POSIX traditional Unicode
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147 | [:digit:] \d \p{IsDigit}
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148 | [:^digit:] \D \P{IsDigit}
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149 |
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150 | =head2 ANCHORS
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151 |
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152 | All are zero-width assertions.
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153 |
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154 | ^ Match string start (or line, if /m is used)
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155 | $ Match string end (or line, if /m is used) or before newline
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156 | \b Match word boundary (between \w and \W)
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157 | \B Match except at word boundary (between \w and \w or \W and \W)
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158 | \A Match string start (regardless of /m)
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159 | \Z Match string end (before optional newline)
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160 | \z Match absolute string end
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161 | \G Match where previous m//g left off
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162 |
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163 | =head2 QUANTIFIERS
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164 |
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165 | Quantifiers are greedy by default -- match the B<longest> leftmost.
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166 |
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167 | Maximal Minimal Allowed range
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168 | ------- ------- -------------
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169 | {n,m} {n,m}? Must occur at least n times but no more than m times
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170 | {n,} {n,}? Must occur at least n times
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171 | {n} {n}? Must occur exactly n times
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172 | * *? 0 or more times (same as {0,})
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173 | + +? 1 or more times (same as {1,})
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174 | ? ?? 0 or 1 time (same as {0,1})
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175 |
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176 | There is no quantifier {,n} -- that gets understood as a literal string.
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177 |
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178 | =head2 EXTENDED CONSTRUCTS
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179 |
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180 | (?#text) A comment
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181 | (?imxs-imsx:...) Enable/disable option (as per m// modifiers)
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182 | (?=...) Zero-width positive lookahead assertion
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183 | (?!...) Zero-width negative lookahead assertion
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184 | (?<=...) Zero-width positive lookbehind assertion
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185 | (?<!...) Zero-width negative lookbehind assertion
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186 | (?>...) Grab what we can, prohibit backtracking
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187 | (?{ code }) Embedded code, return value becomes $^R
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188 | (??{ code }) Dynamic regex, return value used as regex
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189 | (?(cond)yes|no) cond being integer corresponding to capturing parens
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190 | (?(cond)yes) or a lookaround/eval zero-width assertion
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191 |
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192 | =head2 VARIABLES
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193 |
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194 | $_ Default variable for operators to use
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195 | $* Enable multiline matching (deprecated; not in 5.9.0 or later)
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196 |
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197 | $& Entire matched string
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198 | $` Everything prior to matched string
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199 | $' Everything after to matched string
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200 |
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201 | The use of those last three will slow down B<all> regex use
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202 | within your program. Consult L<perlvar> for C<@LAST_MATCH_START>
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203 | to see equivalent expressions that won't cause slow down.
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204 | See also L<Devel::SawAmpersand>.
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205 |
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206 | $1, $2 ... hold the Xth captured expr
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207 | $+ Last parenthesized pattern match
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208 | $^N Holds the most recently closed capture
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209 | $^R Holds the result of the last (?{...}) expr
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210 | @- Offsets of starts of groups. $-[0] holds start of whole match
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211 | @+ Offsets of ends of groups. $+[0] holds end of whole match
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212 |
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213 | Captured groups are numbered according to their I<opening> paren.
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214 |
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215 | =head2 FUNCTIONS
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216 |
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217 | lc Lowercase a string
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218 | lcfirst Lowercase first char of a string
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219 | uc Uppercase a string
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220 | ucfirst Titlecase first char of a string
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221 |
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222 | pos Return or set current match position
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223 | quotemeta Quote metacharacters
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224 | reset Reset ?pattern? status
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225 | study Analyze string for optimizing matching
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226 |
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227 | split Use regex to split a string into parts
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228 |
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229 | The first four of these are like the escape sequences C<\L>, C<\l>,
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230 | C<\U>, and C<\u>. For Titlecase, see L</Titlecase>.
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231 |
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232 | =head2 TERMINOLOGY
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233 |
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234 | =head3 Titlecase
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235 |
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236 | Unicode concept which most often is equal to uppercase, but for
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237 | certain characters like the German "sharp s" there is a difference.
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238 |
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239 | =head1 AUTHOR
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240 |
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241 | Iain Truskett.
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242 |
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243 | This document may be distributed under the same terms as Perl itself.
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244 |
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245 | =head1 SEE ALSO
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246 |
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247 | =over 4
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248 |
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249 | =item *
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250 |
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251 | L<perlretut> for a tutorial on regular expressions.
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252 |
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253 | =item *
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254 |
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255 | L<perlrequick> for a rapid tutorial.
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256 |
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257 | =item *
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258 |
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259 | L<perlre> for more details.
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260 |
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261 | =item *
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262 |
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263 | L<perlvar> for details on the variables.
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264 |
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265 | =item *
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266 |
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267 | L<perlop> for details on the operators.
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268 |
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269 | =item *
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270 |
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271 | L<perlfunc> for details on the functions.
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272 |
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273 | =item *
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274 |
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275 | L<perlfaq6> for FAQs on regular expressions.
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276 |
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277 | =item *
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278 |
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279 | The L<re> module to alter behaviour and aid
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280 | debugging.
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281 |
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282 | =item *
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283 |
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284 | L<perldebug/"Debugging regular expressions">
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285 |
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286 | =item *
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287 |
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288 | L<perluniintro>, L<perlunicode>, L<charnames> and L<locale>
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289 | for details on regexes and internationalisation.
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290 |
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291 | =item *
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292 |
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293 | I<Mastering Regular Expressions> by Jeffrey Friedl
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294 | (F<http://regex.info/>) for a thorough grounding and
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295 | reference on the topic.
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296 |
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297 | =back
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298 |
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299 | =head1 THANKS
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300 |
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301 | David P.C. Wollmann,
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302 | Richard Soderberg,
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303 | Sean M. Burke,
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304 | Tom Christiansen,
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305 | Jim Cromie,
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306 | and
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307 | Jeffrey Goff
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308 | for useful advice.
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309 |
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310 | =cut
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