Regular Expressions 101

Save & Share

Flavor

  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python
  • Golang
  • Java 8
  • .NET 7.0 (C#)
  • Rust
  • Regex Flavor Guide

Function

  • Match
  • Substitution
  • List
  • Unit Tests

Tools

Sponsors
There are currently no sponsors. Become a sponsor today!
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

/
/
gm

Test String

Code Generator

Language

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"l4.2" test_str = ("// Lab 4.2\n" "#include <iostream>\n" "#include <string>\n\n" "using namespace std;\n\n" "string s1, s2;\n\n" "int checkChar() {\n" " int i, len;\n\n" " len = s2.length();\n" " for (i = 0; i < len; i++)\n" " if (s2[i] - 48 < 0 || s2[i] - 48 > 9)\n" " return 0;\n\n" " return 1;\n" "}\n\n" "void inputString() {\n" " cout << \" - Nhap chuoi S1: \";\n" " getline(cin, s1);\n" " \n" " while (1) {\n" " cout << \" - Nhap chuoi S2: \";\n" " getline(cin, s2);\n\n" " if (!checkChar())\n" " cout << \" => \" << \"Input Validation\" << endl << endl;\n" " else\n" " break;\n" " }\n" "}\n\n" "int checkNumber() {\n" " int i, len;\n" " len = s1.length();\n\n" " for (i = 0; i < len; i++)\n" " if (s1[i] - 48 >= 0 && s1[i] - 48 <= 9)\n" " return 1;\n\n" " return 0;\n" "}\n\n" "int checkSDTMobifone() {\n" " int i, len;\n" " len = s2.length();\n\n" " if (len==10 && s2[0] - 48 == 0 && s2[1] - 48 == 9 && s2[2] - 48 == 0) {\n" " for (i = 3; i < 10; i++) {\n" " if (s2[i] - 48 < 0 || s2[i] - 48 > 9)\n" " return 0;\n" " }\n" " return 1;\n" " }\n" " else\n" " return 0;\n" "}\n\n" "int checkSubString() {\n" " int i, j;\n" " int len, len_s1, len_s2, flag;\n" " char temp;\n\n" " len_s1 = s1.length();\n" " len_s2 = s2.length();\n\n" " if (len_s2 == 0)\n" " return 1;\n\n" " if (len_s1 >= len_s2) {\n" " for (i = 0; i <= len_s1 - len_s2; i++) {\n" " flag = 1;\n" " for (j = 0; flag&&j < len_s2; j++) {\n" " if (s1[i + j] != s2[j])\n" " flag = 0;\n" " }\n" " if (flag)\n" " return 1;\n" " }\n" " }\n" " \n" " return 0;\n" "}\n\n" "string addString(){\n" " string s3;\n" " int i, len_s1, len_s2, len;\n\n" " len_s1 = s1.length();\n" " len_s2 = s2.length();\n" " len = len_s1 + len_s2;\n\n" " for (i = 0; i < len; i++) {\n" " if (i < len_s1)\n" " s3 += s1[i];\n" " else\n" " s3 += s2[i - len_s1];\n" " }\n\n" " return s3;\n" "}\n\n" "void insertString(string s3) {\n" " string str_Insert = \"Buffer_Overflow\";\n" " char after;\n" " int i, len, flag;\n\n" " len = s3.length();\n\n" " cout << \" - Chuoi S3: \" << s3 << endl;\n\n" " cout << \" - Ban muon them vao sau ky tu nao: \";\n" " cin >> after;\n\n" " cout << endl << \" => \";\n\n" " flag = 0;\n" " for (i = 0; i < len; i++) {\n" " if (s3[i] != after) {\n" " cout << s3[i];\n" " }\n" " else {\n" " cout << after << str_Insert;\n" " flag++;\n" " }\n" " }\n\n" " if (!flag)\n" " cout << str_Insert << endl;\n" "}\n\n" "int main() {\n\n" " string s1, s2, s3;\n" " // Cau 1\n" " cout << endl << \"Cau 1: \" << endl;\n" " inputString();\n\n" " // Cau 2\n" " cout << endl << \"Cau 2: \" << endl;\n" " if (checkNumber())\n" " cout << \" - Chuoi S1 co chu so\" << endl;\n" " else\n" " cout << \" - Chuoi S1 khong co chu so\" << endl;\n\n" " // Cau 3\n" " cout << endl << \"Cau 3: \" << endl;\n" " if (checkSDTMobifone())\n" " cout << \" - Chuoi S2 la SDT mang Mobifone\" << endl;\n" " else\n" " cout << \" - Chuoi S2 khong la SDT mang Mobifone\" << endl;\n\n" " // Cau 4\n" " cout << endl << \"Cau 4: \" << endl;\n" " if (checkSubString())\n" " cout << \" - Chuoi S2 la tap con cua chuoi S1\" << endl;\n" " else\n" " cout << \" - Chuoi S2 khong la tap con cua chuoi S1\" << endl;\n\n" " // Cau 5\n" " cout << endl << \"Cau 5: \" << endl;\n" " cout << \" - Chuoi S3 = S1 + S2: \";\n" " s3 = addString();\n" " cout << s3 << endl;\n\n" " // Cau 6\n" " cout << endl << \"Cau 6: \" << endl;\n" " insertString(s3);\n" " cout << endl << endl;\n\n\n" " //system(\"pause\");\n" " \n" " return 0;\n" "}\n") matches = re.finditer(regex, test_str, re.MULTILINE) for matchNum, match in enumerate(matches, start=1): print ("Match {matchNum} was found at {start}-{end}: {match}".format(matchNum = matchNum, start = match.start(), end = match.end(), match = match.group())) for groupNum in range(0, len(match.groups())): groupNum = groupNum + 1 print ("Group {groupNum} found at {start}-{end}: {group}".format(groupNum = groupNum, start = match.start(groupNum), end = match.end(groupNum), group = match.group(groupNum))) # Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

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