Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/
gs

Test String

Code Generator

Language

Generated Code

use strict; my $str = 'Remove comments from some generated HTML which can be invalid with nested comments ================================================================================== I would like to remove HTML comments from some generated content. If I use the regex `/<!--(.*?)-->/` (ungreedy with the `?`) then it works for most cases such as this example: ```html <!-- <h1> test </h1> --> not remove <!-- <h1> test 2 </h1> --> ``` It gets rid of the `<h1>` tags and leaves the "*not remove*" as desired. But **if the comments are nested**, then it will not handle it properly as it will leave the last comment closing tag `\'-->\'`. The workaround would be to use a greedy pattern, but in this case it will not work for the first case, with multiple comments. Example of nested comments (I know it\'s not valid HTML, but it\'s the backend which is generating it): ```html text <!-- something <!-- <p> test </p> --> need remove --> ``` I\'ve tried to find a solution, but I don\'t know how to solve this. Has anyone an idea how to handle it? <!-- multiline comment --> <!-- <footer>Footer with nested <!-- comment --> on several lines.</footer> -->'; my $regex = qr/<!--(?:(?!<!--|-->).|(?R))*-->/sp; if ( $str =~ /$regex/g ) { print "Whole match is ${^MATCH} and its start/end positions can be obtained via \$-[0] and \$+[0]\n"; # print "Capture Group 1 is $1 and its start/end positions can be obtained via \$-[1] and \$+[1]\n"; # print "Capture Group 2 is $2 ... and so on\n"; } # ${^POSTMATCH} and ${^PREMATCH} are also available with the use of '/p' # Named capture groups can be called via $+{name}

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html