Regular Expressions 101

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  • All Tokens
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  • 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
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Test String

Code Generator

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Generated Code

import re regex = re.compile(r"back up code", flags=re.MULTILINE) test_str = ("//9-digits phone number\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " int n;\n" " string s;\n" " cin >> n;\n" " getline(cin,s);\n" " while(n--){\n" " regex phone10(\"09[0-9]{2}(\\\\.[0-9]{3}){2}\");\n" " string st;\n" " getline(cin, st);\n" " if(regex_match(st, phone10))\n" " cout << \"Valid!\" << endl;\n" " else\n" " cout << \"Invalid!\" << endl;\n" " }\n" " \n" " return 0;\n" "}\n\n\n\n" "//11 digits phone number\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " regex phone10(\"01[0-9]{9}\");\n" " string st;\n" " int n;\n" " cin >> n;\n" " getline(cin,st);\n" " while(n--){\n" " getline(cin, st);\n" " if(regex_match(st, phone10))\n" " cout << \"Valid!\" << endl;\n" " else\n" " cout << \"Invalid!\" << endl;\n" " }\n" " \n" " return 0;\n" "}\n\n\n\n" "//alphabet string\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " regex pattern(\"[a-zA-Z\\\\s]+\");\n" " string st;\n" " int n;\n" " cin >> n;\n" " getline(cin,st);\n" " while(n--){\n" " getline(cin, st);\n" " if(regex_match(st, pattern))\n" " cout << \"Valid!\" << endl;\n" " else\n" " cout << \"Invalid!\" << endl;\n" " }\n" " \n" " return 0;\n" "}\n\n\n\n" "//Alpha-numberic Strings With Limited Length\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " regex pattern(\"[a-z0-9]{6,20}\");\n" " string st;\n" " int n;\n" " cin >> n;\n" " getline(cin,st);\n" " while(n--){\n" " getline(cin, st);\n" " if(regex_match(st, pattern))\n" " cout << \"Valid!\" << endl;\n" " else\n" " cout << \"Invalid!\" << endl;\n" " }\n" " \n" " return 0;\n" "}\n\n\n\n" "//bound checking for a Product\n" "#include <stdio.h>\n" "#include <stdlib.h>\n" "#include <limits.h>\n\n" "int main()\n" "{\n" " unsigned int a,b;\n" " scanf(\"%u%u\",&a,&b);\n" " if(a!=0 && b!=0 && UINT_MAX/a<b)\n" " printf(\"No\");\n" " else\n" " printf(\"Yes\");\n" "}\n\n\n\n" "//bound checking for a Signed Product\n" "#include <stdio.h>\n" "#include <stdlib.h>\n" "#include <limits.h>\n\n" "int main()\n" "{\n" " int a,b;\n" " scanf(\"%d%d\",&a,&b);\n" " if(a>0&&b>0){\n" " if(INT_MAX/a<b)\n" " printf(\"No\");\n" " else\n" " printf(\"Yes\");\n" " }\n" " else if(a<0&&b<0){\n" " if(INT_MAX/b>a)\n" " printf(\"No\");\n" " else\n" " printf(\"Yes\");\n" " }\n" " else if(a>0&&b<0){\n" " if(INT_MIN/a>b)\n" " printf(\"No\");\n" " else\n" " printf(\"Yes\");\n" " }\n" " else if(a<0&&b>0){\n" " if(INT_MIN/b>a)\n" " printf(\"No\");\n" " else\n" " printf(\"Yes\");\n" " }\n" " else\n" " printf(\"Yes\");\n\n" "}\n\n\n\n" "//bound checking for a Signed sum\n" "#include <stdio.h>\n" "#include <stdlib.h>\n" "#include <limits.h>\n\n" "int main()\n" "{\n" " int a,b;\n" " scanf(\"%d%d\",&a,&b);\n" " if(a>0 && b>0 && b>INT_MAX-a)\n" " printf(\"No\");\n" " else if(a<0 && b<0 && b<INT_MIN-a)\n" " printf(\"No\");\n" " else\n" " printf(\"Yes\");\n" "}\n\n\n\n" "//Bound checking for a Sum\n" "#include <stdio.h>\n" "#include <stdlib.h>\n" "#include <limits.h>\n\n" "int main()\n" "{\n" " unsigned int a,b;\n" " scanf(\"%u%u\",&a,&b);\n" " if(UINT_MAX-a>=b)\n" " printf(\"Yes\");\n" " else\n" " printf(\"No\");\n" "}\n\n\n" "//bound checking for an Integer\n" "#include <stdio.h>\n" "#include <stdlib.h>\n" "#include <string.h>\n\n" "int main()\n" "{\n" " char *s1 = (char*)malloc(12*sizeof(char));\n" " char *s2 = (char*)malloc(12*sizeof(char));\n" " gets(s1);\n" " int a = atoi(s1);\n" " sprintf(s2,\"%d\",a);\n" " if(strcmp(s1,s2)==0)\n" " printf(\"Yes\");\n" " else\n" " printf(\"No\");\n\n" "}\n\n" "//bound checking for the LCM\n" "#include <stdio.h>\n" "#include <stdlib.h>\n" "#include <limits.h>\n\n" "unsigned long long gcd(unsigned long long a, unsigned long long b) {\n" " unsigned long long temp = 0;\n" " while (b != 0)\n" " {\n" " temp = a % b;\n" " a = b;\n" " b = temp;\n" " }\n" " return a;\n" "}\n\n" "int main(void) {\n" " unsigned long long a, b;\n" " scanf(\"%llu %llu\", &a, &b);\n\n" " unsigned long long UCLN = gcd(a,b);\n" " if(a==0||b==0)\n" " printf(\"N/A\");\n" " else if((a/UCLN) <= (ULLONG_MAX/b))\n" " printf(\"%llu\",a/UCLN*b);\n" " else{\n" " printf(\"N/A\");\n" " }\n\n" " return 0;\n" "}\n\n\n\n\n" "//dual format telephone number\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " regex phone10(\"(\\\\+84|0)1[0-9]{9}\");\n" " string st;\n" " int n;\n" " cin >> n;\n" " getline(cin,st);\n" " while(n--){\n" " getline(cin, st);\n" " if(regex_match(st, phone10))\n" " cout << \"Valid!\" << endl;\n" " else\n" " cout << \"Invalid!\" << endl;\n" " }\n" " \n" " return 0;\n" "}\n\n\n\n\n" "//email address\n" "#include <iostream>\n" "#include <regex>\n" "#include <string>\n" "using namespace std;\n\n" "int main(){\n" " regex pattern(\"([\\\\w!#$%&'*+/=?^_`{|}~-]+\\\\.?[\\\\w!#$%&'*+/=?^_`{|}~-]+)+@(\\\\w+(\\\\-\\\\w+)?(\\\\.\\\\w+))+\");\n" " int x;\n" " cin >>x;\n" " string line_;\n" " getline(cin,line_);\n" " while(x--){\n" " getline(cin,line_);\n" " if(regex_match(line_,pattern))\n" " cout << \"Valid!\"<<endl;\n" " else\n" " cout <<\"Invalid!\"<<endl;\n" " }\n" " return 0;\n" "}\n\n\n\n" "//find IP attack\n" "#include <iostream>\n" "#include <regex>\n" "#include <string>\n" "using namespace std;\n\n" "int main(){\n" " regex pattern(\"\\\\d+\\\\ \\\\d+\\\\.\\\\d+(\\\\ ((25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9][0-9]|[0-9])\\\\.){3}(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9][0-9]|[0-9])){2}\\\\ [A-Z]+\\\\ \\\\d+ [A-Z]+\\\\ [\\\\w-+/?=&.: ]+\");\n" " int t;\n" " string st;\n" " cin >> t;\n" " getline(cin, st);\n" " int i = 1;\n" " while(t--){\n" " getline(cin, st);\n" " cout << i++ << endl;\n" " sregex_token_iterator pos(st.cbegin(),st.cend(), pattern, 0);\n" " sregex_token_iterator end;\n" " for (; pos!=end; ++pos)\n" " cout << \"Found \" << pos->str() << endl;\n" " }\n" " return 0;\n" "}\n\n\n\n" "//integer number\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " regex pattern(\"[\\\\+-]?[1-9][0-9]*\");\n" " string st;\n" " int n;\n" " cin >> n;\n" " getline(cin,st);\n" " while(n--){\n" " getline(cin, st);\n" " if(regex_match(st, pattern))\n" " cout << \"Valid!\" << endl;\n" " else\n" " cout << \"Invalid!\" << endl;\n" " }\n" " \n" " return 0;\n" "}\n\n\n\n\n" "//list email in raw data\n" "#include <iostream>\n" "#include <regex>\n" "#include <string>\n" "using namespace std;\n\n" "int main(){\n" " regex pattern(\"([\\\\w_-]+(\\\\.?[\\\\w_-]))+@[\\\\w]+([_\\\\w]+)?(\\\\.[\\\\w]+)+\");\n" " int t;\n" " string st;\n" " cin >> t;\n" " getline(cin, st);\n" " int i = 1;\n" " while(t--){\n" " getline(cin, st);\n" " cout << i++ << endl;\n" " sregex_token_iterator pos(st.cbegin(),st.cend(), pattern, 0);\n" " sregex_token_iterator end;\n" " for (; pos!=end; ++pos)\n" " cout << \"Found \" << pos->str()<< endl;\n" " }\n" " return 0;\n" "}\n\n\n\n\n" "//list IP in log web\n" "#include <iostream>\n" "#include <regex>\n" "#include <string>\n" "using namespace std;\n\n" "int main(){\n" " regex pattern(\"((25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9][0-9]|[0-9])\\\\.){3}(25[0-5]|2[0-4][0-9]|1[0-9]{2}|[1-9][0-9]|[0-9])\");\n" " int t;\n" " string st;\n" " cin >> t;\n" " getline(cin, st);\n" " int i = 1;\n" " while(t--){\n" " getline(cin, st);\n" " cout << i++ << endl;\n" " sregex_token_iterator pos(st.cbegin(),st.cend(), pattern, 0);\n" " sregex_token_iterator end;\n" " for (; pos!=end; ++pos)\n" " cout << \"Found \" << pos->str()<< endl;\n" " }\n" " return 0;\n" "}\n\n\n\n\n" "//list link in a tag HTML\n" "#include <iostream>\n" "#include <regex>\n" "#include <string>\n" "using namespace std;\n\n" "int main(){\n" " regex pattern(\"(http|https|ftp)://[\\\\w\\\\.]+([-\\\\w\\\\.]+)?(:\\\\d+)?([/\\\\w]+)?\");\n" " int t;\n" " string st;\n" " cin >> t;\n" " getline(cin, st);\n" " int i = 1;\n" " while(t--){\n" " getline(cin, st);\n" " cout << i++ << endl;\n" " sregex_token_iterator pos(st.cbegin(),st.cend(), pattern, 0);\n" " sregex_token_iterator end;\n" " for ( ; pos!=end ; ++pos )\n" " cout << \"Found: \" << pos->str()<< endl;\n" " }\n" " return 0;\n" "}\n\n\n\n" "//list phone number\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " regex pattern(\"((\\\\+84)|0)[1-9][0-9]{8,9}\");\n" " string st;\n" " int n;\n" " cin >> n;\n" " getline(cin, st);\n" " for(int i=1;i<=n;i++){\n" " cout << i << endl;\n" " getline(cin, st);\n" " sregex_token_iterator pos(st.cbegin(),st.cend(), pattern, 0);\n" " sregex_token_iterator end;\n" " for ( ; pos!=end ; ++pos ) {\n" " cout << \"Found \" << pos->str() << \" at \" << pos->first-st.begin() << endl;\n" " }\n" " } \n" " return 0;\n" "}\n\n\n\n" "//matching specific FileName\n" "#include <iostream>\n" "#include <regex>\n" "#include <string>\n" "using namespace std;\n\n" "int main(){\n" " regex images(\"[a-zA-Z0-9\\\\_\\\\.]+\\\\.?[a-zA-Z0-9\\\\_]+\\\\.(([jJ][pP][gG])|([pP][nN][gG])|([gG][iI][fF]))\");\n" " regex docs(\"[a-zA-Z0-9\\\\_\\\\.]+\\\\.?[a-zA-Z0-9\\\\_]+\\\\.(([pP][dD][f|])|([dD][oO][cC])|([pP]{2}[tT][xX]))\");\n" " regex media(\"[a-zA-Z0-9\\\\_\\\\.]+\\\\.?[a-zA-Z0-9\\\\_]+\\\\.(([m|M][p|P][3|4])|([a|A][v|V][i|I]))\");\n" " int t;\n" " string st;\n" " cin >> t;\n" " getline(cin, st);\n" " int i = 1;\n" " while(t--){\n" " getline(cin, st);\n" " cout << i++ << endl;\n" " \n" " sregex_token_iterator pos(st.cbegin(),st.cend(), images, 0);\n" " sregex_token_iterator end;\n" " for ( ; pos!=end ; ++pos )\n" " cout << pos->str() << \" : \" << \"hinh anh\" << endl;\n" " \n" " sregex_token_iterator pos1(st.cbegin(),st.cend(), media, 0);\n" " sregex_token_iterator end1;\n" " for ( ; pos1!=end1 ; ++pos1 )\n" " cout << pos1->str() << \" : \" << \"media\" << endl;\n" " \n" " sregex_token_iterator pos2(st.cbegin(),st.cend(), docs, 0);\n" " sregex_token_iterator end2;\n" " for ( ; pos2!=end2 ; ++pos2 )\n" " cout << pos2->str() << \" : \" << \"tai lieu\" << endl;\n" " }\n" " return 0;\n" "}\n\n\n\n\n" "//modify telephone number\n" "#include <iostream>\n" "#include <regex>\n" "#include <string>\n" "using namespace std;\n\n" "string Convert(string str){\n" " string temp = \"\";\n" " string sub = str.substr(0,4);\n" " if(sub.compare(\"0123\") ==0){\n" " regex at_sign(\"0123\");\n" " string replace_by(\"083\");\n" " temp = regex_replace(str, at_sign, replace_by);\n" " }else if(sub.compare(\"0124\") ==0){\n" " regex at_sign(\"0124\");\n" " string replace_by(\"084\");\n" " temp = regex_replace(str, at_sign, replace_by);\n" " }else if(sub.compare(\"0125\") ==0){\n" " regex at_sign(\"0125\");\n" " string replace_by(\"085\");\n" " temp = regex_replace(str, at_sign, replace_by);\n" " }\n" " else if(sub.compare(\"0127\") ==0){\n" " regex at_sign(\"0127\");\n" " string replace_by(\"081\");\n" " temp = regex_replace(str, at_sign, replace_by);\n" " }\n" " else if(sub.compare(\"0129\") ==0){\n" " regex at_sign(\"0129\");\n" " string replace_by(\"082\");\n" " temp = regex_replace(str, at_sign, replace_by);\n" " }\n" " return temp;\n" "}\n" "int main(){\n" " regex pattern(\"012[3-9^6]\\\\d{7}\");\n" " int t;\n" " string st;\n" " cin >> t;\n" " getline(cin, st);\n\n" " for(int i = 1; i <= t ; i++){\n" " getline(cin, st);\n" " cout << i << endl;\n" " sregex_token_iterator pos(st.cbegin(),st.cend(), pattern, 0);\n" " sregex_token_iterator end;\n" " for (; pos!=end; ++pos){\n" " string str1 = pos->str();\n" " cout << \"Thay doi: \" << Convert(str1) << endl;\n" " }\n" " }\n" " return 0;\n" "}\n\n\n\n" "//numeric string leading without zero\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " regex pattern(\"[1-9][0-9]*\");\n" " string st;\n" " int n;\n" " cin >> n;\n" " getline(cin,st);\n" " while(n--){\n" " getline(cin, st);\n" " if(regex_match(st, pattern))\n" " cout << \"Valid!\" << endl;\n" " else\n" " cout << \"Invalid!\" << endl;\n" " }\n" " \n" " return 0;\n" "}\n\n\n\n\n" "//numeric string\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " regex pattern(\"[0-9]*\");\n" " string st;\n" " int n;\n" " cin >> n;\n" " getline(cin,st);\n" " while(n--){\n" " getline(cin, st);\n" " if(regex_match(st, pattern))\n" " cout << \"Valid!\" << endl;\n" " else\n" " cout << \"Invalid!\" << endl;\n" " }\n" " \n" " return 0;\n" "}\n\n\n\n\n" "//telephone number international format\n" "#include<iostream>\n" "#include<regex>\n" "#include <string>\n" "#include <stdexcept>\n" "using namespace std;\n" "int main()\n" "{\n" " regex phone10(\"\\\\+841(\\\\.[0-9]{3}){3}\");\n" " string st;\n" " int n;\n" " cin >> n;\n" " getline(cin,st);\n" " while(n--){\n" " getline(cin, st);\n" " if(regex_match(st, phone10))\n" " cout << \"Valid!\" << endl;\n" " else\n" " cout << \"Invalid!\" << endl;\n" " }\n" " \n" " return 0;\n" "}\n\n\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