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

/
/
gmx

Test String

Code Generator

Language

Generated Code

const regex = /(?<=^|,|\w[ ])[ ]*\K(?!<[^.#])MY_STRING(?=[^.#])[ ]*(?=,|$) |(?<=%)MY_STRING(?=%)|(?<=\()MY_STRING(?=\)) |(?:^|\w[ ]*)\KMY_STRING(?=[ ]*;comment) |,[ ]*(%)?MY_STRING\1[^,]+;comment(*SKIP)(*FAIL) |(^.*;video[ ]*$)(*SKIP)(*FAIL)/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?<=^|,|\\w[ ])[ ]*\\K(?!<[^.#])MY_STRING(?=[^.#])[ ]*(?=,|$) |(?<=%)MY_STRING(?=%)|(?<=\\()MY_STRING(?=\\)) |(?:^|\\w[ ]*)\\KMY_STRING(?=[ ]*;comment) |,[ ]*(%)?MY_STRING\\1[^,]+;comment(*SKIP)(*FAIL) |(^.*;video[ ]*$)(*SKIP)(*FAIL)', 'gm') const str = `[1] text,MY_STRING ;comment text,MY_STRING text ;comment text,text MY_STRING text ;comment -------------------------------------------------------------- -> dont catch any above because exist a **comma** before #MY_STRING# and ;comment after. -------------------------------------------------------------- [2] text, MY_STRING , text ;comment -------------------------------------------------------------- -> catch because exist a **comma** after #MY_STRING# -------------------------------------------------------------- [3] text, MY_STRING, MY_STRING ;comment -------------------------------------------------------------- -> catch first #MY_STRING# but don't catch last #MY_STRING# because she is between , and ;comment -------------------------------------------------------------- [4] MY_STRING MY_STRING,text text, MY_STRING, MY_STRING ;comment text MY_STRING ;comment text,MY_STRING,text ;comment %MY_STRING% , (MY_STRING) -------------------------------------------------------------- -> catch all, because there's no [comma . #] preceding #MY_STRING# and no [# ;comment ;video] succeeding -------------------------------------------------------------- [5] .MY_STRING #MY_STRING MY_STRING# -------------------------------------------------------------- - > dont catch any Independent of where MY_STRING is, either what it has between, don't catch any, because they have . or # preceding/proceeding the string. -------------------------------------------------------------- [6] MY_STRING, .MY_STRING, #MY_STRING, text, MY_STRING text, MY_STRING#, MY_STRING, .MY_STRING -------------------------------------------------------------- -> same as above, just catch MY_STRING samples not containing . # -------------------------------------------------------------- [7] text, MY_STRING ;video MY_STRING ;video #MY_STRING, MY_STRING, text, text MY_STRING ;video -------------------------------------------------------------- - > In this case, the string will not be caught independent of where it is or what it has preceding/succeeding because exist the string ;video at the ending. -------------------------------------------------------------- [8] text,MY_STRING, text ;comment ^ ok catch (reason explained above) -------------------------------------------------------------- [9] text,MY_STRING@ text ;comment -------------------------------------------------------------- ^ dont catch, because there's no comma after the string, and there's a comma before and ;comment after -------------------------------------------------------------- [10] MY_STRING,text,#MY_STRING,text,text,%MY_STRING% @ \$text #text <text> ;comment ^[1] ^[2] ^[3] -------------------------------------------------------------- [1] catch [2] don't (# preceding) [3] don't catch, because there's a comma preceding, no comma succeding and at the end line exist the string ;comment -------------------------------------------------------------- [11] .MY_STRING,text,MY_STRING,text,text,%MY_STRING% @ \$text, #text <text> ;comment ^[1] ^[2] ^[3] ^[4] -------------------------------------------------------------- [1] don't (dot preceding) [2] catch [3] catch because there's a comma on [4] so the string is not anymore between a comma preceding and ;comment succeeding, she is now between a comma preceding a comma succeeding and ;comment [12] .MY_STRING,text,MY_STRING,text,text,%MY_STRING% @ \$text #text <text> ;comment ^[1] ^[2] ^[3] ^[4] --------------------------------------------------------------`; // Reset `lastIndex` if this regex is defined globally // regex.lastIndex = 0; let m; while ((m = regex.exec(str)) !== null) { // This is necessary to avoid infinite loops with zero-width matches if (m.index === regex.lastIndex) { regex.lastIndex++; } // The result can be accessed through the `m`-variable. m.forEach((match, groupIndex) => { console.log(`Found match, group ${groupIndex}: ${match}`); }); }

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 JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions