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
Processing...

Test String

Code Generator

Language

Generated Code

import re regex = re.compile(r"l4.1", flags=re.MULTILINE) test_str = ("// Lab 4.1\n\n\n" "#include <iostream>\n" "#include <stdlib.h>\n\n" "using namespace std;\n\n" "int n, m;\n" "int a[21], b[21], c[42];\n\n" "// Cau 1\n" "void createArray() {\n" " int i;\n\n" " do {\n" " cout << \" - Nhap gia tri cua n: \";\n" " cin >> n;\n" " } while (10 > n || n > 20);\n\n" " // Khoi tao 2 mang A & B co n phan tu\n" " for (i = 0; i < n; i++) {\n" " a[i] = rand() % 490 + 10;\n" " b[i] = rand() % 490 + 10;\n" " }\n" "}\n\n" "void printArray(int *array, int len) {\n" " int i;\n\n" " for (i = 0; i < len; i++) {\n" " cout << \"\\t\" << array[i];\n" " }\n" " cout << endl;\n" "}\n\n" "void chanA_LeB() {\n" " int i, j;\n" " j = 0;\n" " for (i = 0; i < n; i++) {\n" " if (a[i] % 2 == 0) {\n" " c[j] = a[i];\n" " j++;\n" " }\n" " if (b[i] % 2 != 0) {\n" " c[j] = b[i];\n" " j++;\n" " }\n" " }\n" " m = j;\n" "}\n\n" "int mul_is_safe(int a, int b) {\n" " if (b > INT_MAX / a)\n" " return 0;\n" " return 1;\n" "}\n\n" "void mulArray() {\n" " int i, j;\n" " long long KQ;\n" " KQ = 1;\n\n" " for (i = 0; i < m; i++) {\n" " if (mul_is_safe(c[i], KQ)) {\n" " cout << c[i];\n" " KQ *= c[i];\n" " for (j = i-1; j >= 0; j--) {\n" " if (i != 0)\n" " cout << \" * \" << c[j];\n" " }\n" " cout << \" = \" << KQ << endl;\n" " }\n" " else {\n" " cout << \"Integer Overflow\" << endl << endl;\n" " return;\n" " }\n" " }\n" "}\n\n" "int main() {\n\n" " // Cau 1\n" " cout << \"Cau 1: \" << endl;\n" " createArray();\n\n" " // Cau 2\n" " cout << endl << \"Cau 2: \" << endl;\n" " cout << \" - Mang A: \" << endl;\n" " printArray(a, n);\n" " cout << \" - Mang B: \" << endl;\n" " printArray(b, n);\n\n" " // Cau 3\n" " cout << endl << \"Cau 3: \" << endl;\n" " chanA_LeB();\n" " cout << \" - Mang C: \" << endl;\n" " printArray(c, m);\n\n" " // Cau 4\n" " cout << endl << \"Cau 4: \" << endl;\n" " mulArray();\n\n" " //system(\"pause\");\n" " return 0;\n" "}\n") matches = regex.finditer(test_str) for match_num, match in enumerate(matches, start=1): print(f"Match {match_num} was found at {match.start()}-{match.end()}: {match.group()}") for group_num, group in enumerate(match.groups(), start=1): print(f"Group {group_num} found at {match.start(group_num)}-{match.end(group_num)}: {group}")

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 Python, please visit: https://docs.python.org/3/library/re.html