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

/
/
g

Test String

Substitution

Processing...

Code Generator

Language

Generated Code

$re = '/\[\[(?:[^][]*|\[(?!\[)|\](?!\]))*+\]\]\K|\[\[ ?| ?\]\]/'; $str = 'Locate instances of nested double square brackets and remove the outer double square brackets I\'m using TextMate (but happy to use any suitable search and replace program) to query a set of files (these files are my notes in Logseq if its relevant). I\'m looking to find and replace instances of nested double square brackets and remove the outer double square brackets eg 1 - Normal nesting [[ any text or no text [[ any text ]] any text or no text]] eg 2 - Compound nesting [[ any text or no text [[ any text ]] [[ any text ]] any text or not text ]] eg 3 - multi-level nesting [[ any text or no text [[ any text or no text [[ any text or no text ]] any text or no text]] any text or no text ]] Note: keep in mind that the double square brackets could be touching. So example 1 could also manifest as [[ any text or no text [[ any text ]]]]'; $subst = ""; $result = preg_replace($re, $subst, $str); echo "The result of the substitution is ".$result;

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 PHP, please visit: http://php.net/manual/en/ref.pcre.php