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

/
/
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"([\r\n]+)(?=[A-Z][a-z]{2}\s+\d{1,2}\s\d{2}:\d{2}:\d{2}\s)" test_str = ("Jun 26 13:46:12 128.23.84.166 [local0.err] <131>Jun 26 13:46:12 GBSDFA1AD011HMA.systems.uk.fed ASM:f5_asm=PROD\n\n" "vs_name=\"/f5-tenant-01/XXXXXXXX\"\n" "violations=\"HTTP protocol compliance failed\"\n" "sub_violations=\"HTTP protocol compliance failed:Header name with no header value\"\n" "attack_type=\"HTTP Parser Attack\"\n" "violation_rating=\"3/5\"\n" "severity=\"Error\"\n\n" "support_id=\"XXXXXXXXX\"\n" "policy_name=\"/Common/waf-fed-transparent\"\n" "enforcement_action=\"none\"\n\n" "dest_ip_port=\"128.155.6.2:443\"\n" "ip_client=\"128.163.192.44\"\n" "x_forwarded_for_header_value=\"N/A\"\n\n" "method=\"POST\"\n" "uri=\"/auth-service/api/v2/token/refreshAccessToken\"\n" "microservice=\"N/A\"\n" "query_string=\"N/A\"\n" "response_code=\"500\"\n\n" "sig_cves=\"N/A\"\n" "sig_ids=\"N/A\"\n" "sig_names={N/A}\n" "sig_set_names=\"N/A\"\n" "staged_sig_cves=\"N/A\"\n" "staged_sig_ids=\"N/A\"\n" "staged_sig_names=\"N/A\"\n" "staged_sig_set_names=\"N/A\"\n\n" "<?xml version='1.0' encoding='UTF-8'?>\n" "<BAD_MSG>\n" "<violation_masks>\n" "<block>0-0-0-0</block>\n" "<alarm>2400500004500-106200000003e-0-0</alarm>\n" "<learn>0-0-0-0</learn>\n" "<staging>0-0-0-0</staging>\n" "</violation_masks>\n" "<request-violations>\n" "<violation>\n" "<viol_index>14</viol_index>\n" "<viol_name>VIOL_HTTP_PROTOCOL</viol_name>\n" "<http_sanity_checks_status>2</http_sanity_checks_status>\n" "<http_sub_violation_status>2</http_sub_violation_status>\n" "<http_sub_violation>SGVhZGVyICdBdXRob3JpemF0aW9uJyBoYXMgbm8gdmFsdWU=</http_sub_violation>\n" "</violation>\n" "</request-violations>\n" "</BAD_MSG>\n" "Jun 26 13:40:31 128.168.189.4 [local0.err] <131>2025-06-26T13:40:31+00:00 nginxplus-nginx-ingress-controller-6498464cd4-k57b5 ASM:attack_type=\"Cross Site Scripting (XSS)\",blocking_exception_reason=\"N/A\",date_time=\"2025-06-26 13:40:31\",dest_port=\"443\",ip_client=\"128.175.220.223\",is_truncated=\"false\",method=\"GET\",policy_name=\"waf-fed-enforced\",protocol=\"HTTPS\",request_status=\"blocked\",response_code=\"0\",severity=\"N/A\",sig_cves=\"N/A,N/A,N/A,N/A\",sig_ids=\"200001475,200000098,200001088,200101609\",sig_names=\"XSS script tag end (Parameter) (2),XSS script tag (Parameter),alert() (Parameter)...\",sig_set_names=\"{High Accuracy Signatures;Cross Site Scripting Signatures;Generic Detection Signatures (High Accuracy)},{High Accuracy Signatures;Cross Site Scripting Signatures;Generic Detection Signatures (High Accuracy)},{Cross Site Scripting Signatures}...\",src_port=\"64344\",sub_violations=\"N/A\",support_id=\"11720398659341069199\",threat_campaign_names=\"N/A\",unit_hostname=\"nginxplus-nginx-ingress-controller-6498464cd4-k57b5\",uri=\"/waf\",violation_rating=\"5\",vs_name=\"14-cyberwasp-sv-helloworld.ikp3001ynp.cloud.uk.fed:24-/waf\",x_forwarded_for_header_value=\"N/A\",outcome=\"REJECTED\",outcome_reason=\"SECURITY_WAF_VIOLATION\",violations=\"Attack signature detected\",json_log=\"{\"\"id\"\":\"\"11720398659341069199\"\",\"\"violations\"\":[{\"\"enforcementState\"\":{\"\"isBlocked\"\":true,\"\"isAlarmed\"\":true,\"\"isInStaging\"\":false,\"\"isLearned\"\":false,\"\"isLikelyFalsePositive\"\":false,\"\"attackType\"\":[{\"\"name\"\":\"\"Cross Site Scripting (XSS)\"\"}]},\"\"violation\"\":{\"\"name\"\":\"\"VIOL_ATTACK_SIGNATURE\"\"},\"\"signature\"\":{\"\"name\"\":\"\"XSS script tag end (Parameter) (2)\"\",\"\"signatureId\"\":200001475,\"\"accuracy\"\":\"\"high\"\",\"\"risk\"\":\"\"high\"\",\"\"hasCve\"\":false,\"\"stagingCertificationDatetime\"\":\"\"1970-01-01T00:00:00Z\"\",\"\"lastUpdateTime\"\":\"\"2025-01-08T16:57:22Z\"\"},\"\"snippet\"\":{\"\"buffer\"\":\"\"c3ZhbmdhPTxzY3JpcHQ+YWxlcnQoMSk8L3NjcmlwdD4i\"\",\"\"offset\"\":8,\"\"length\"\":7},\"\"policyEntity\"\":{\"\"parameters\"\":[{\"\"name\"\":\"\"*\"\",\"\"level\"\":\"\"global\"\",\"\"type\"\":\"\"wildcard\"\"}]},\"\"observedEntity\"\":{\"\"name\"\":\"\"c3Zhbmdh\"\",\"\"value\"\":\"\"PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0PiI=\"\",\"\"location\"\":\"\"query\"\"}},{\"\"enforcementState\"\":{\"\"isBlocked\"\":true,\"\"isAlarmed\"\":true,\"\"isInStaging\"\":false,\"\"isLearned\"\":false,\"\"isLikelyFalsePositive\"\":false,\"\"attackType\"\":[{\"\"name\"\":\"\"Cross Site Scripting (XSS)\"\"}]},\"\"violation\"\":{\"\"name\"\":\"\"VIOL_ATTACK_SIGNATURE\"\"},\"\"signature\"\":{\"\"name\"\":\"\"XSS script tag (Parameter)\"\",\"\"signatureId\"\":200000098,\"\"accuracy\"\":\"\"high\"\",\"\"risk\"\":\"\"high\"\",\"\"hasCve\"\":false,\"\"stagingCertificationDatetime\"\":\"\"1970-01-01T00:00:00Z\"\",\"\"lastUpdateTime\"\":\"\"2023-11-02T19:36:54Z\"\"},\"\"snippet\"\":{\"\"buffer\"\":\"\"c3ZhbmdhPTxzY3JpcHQ+YWxlcnQoMSk8L3NjcmlwdD4i\"\",\"\"offset\"\":7,\"\"length\"\":7},\"\"policyEntity\"\":{\"\"parameters\"\":[{\"\"name\"\":\"\"*\"\",\"\"level\"\":\"\"global\"\",\"\"type\"\":\"\"wildcard\"\"}]},\"\"observedEntity\"\":{\"\"name\"\":\"\"c3Zhbmdh\"\",\"\"value\"\":\"\"PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0PiI=\"\",\"\"location\"\":\"\"query\"\"}},{\"\"enforcementState\"\":{\"\"isBlocked\"\":false,\"\"isAlarmed\"\":true,\"\"isInStaging\"\":false,\"\"isLearned\"\":false,\"\"isLikelyFalsePositive\"\":false,\"\"attackType\"\":[{\"\"name\"\":\"\"Cross Site Scripting (XSS)\"\"}]},\"\"violation\"\":{\"\"name\"\":\"\"VIOL_ATTACK_SIGNATURE\"\"},\"\"signature\"\":{\"\"name\"\":\"\"alert() (Parameter)\"\",\"\"signatureId\"\":200001088,\"\"accuracy\"\":\"\"low\"\",\"\"risk\"\":\"\"medium\"\",\"\"hasCve\"\":false,\"\"stagingCertificationDatetime\"\":\"\"1970-01-01T00:00:00Z\"\",\"\"lastUpdateTime\"\":\"\"2025-03-19T14:09:48Z\"\"},\"\"snippet\"\":{\"\"buffer\"\":\"\"c3ZhbmdhPTxzY3JpcHQ+YWxlcnQoMSk8L3NjcmlwdD4i\"\",\"\"offset\"\":15,\"\"length\"\":6},\"\"policyEntity\"\":{\"\"parameters\"\":[{\"\"name\"\":\"\"*\"\",\"\"level\"\":\"\"global\"\",\"\"type\"\":\"\"wildcard\"\"}]},\"\"observedEntity\"\":{\"\"name\"\":\"\"c3Zhbmdh\"\",\"\"value\"\":\"\"PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0PiI=\"\",\"\"location\"\":\"\"query\"\"}},{\"\"enforcementState\"\":{\"\"isBlocked\"\":true,\"\"isAlarmed\"\":true,\"\"isInStaging\"\":false,\"\"isLearned\"\":false,\"\"isLikelyFalsePositive\"\":false,\"\"attackType\"\":[{\"\"name\"\":\"\"Cross Site Scripting (XSS)\"\"}]},\"\"violation\"\":{\"\"name\"\":\"\"VIOL_ATTACK_SIGNATURE\"\"},\"\"signature\"\":{\"\"name\"\":\"\"\\u003cscript\\u003ealert(1);\\u003c/script\\u003e (Parameter)\"\",\"\"signatureId\"\":200101609,\"\"accuracy\"\":\"\"high\"\",\"\"risk\"\":\"\"high\"\",\"\"hasCve\"\":false,\"\"stagingCertificationDatetime\"\":\"\"1970-01-01T00:00:00Z\"\",\"\"lastUpdateTime\"\":\"\"2020-04-12T21:41:39Z\"\"},\"\"snippet\"\":{\"\"buffer\"\":\"\"c3ZhbmdhPTxzY3JpcHQ+YWxlcnQoMSk8L3NjcmlwdD4i\"\",\"\"offset\"\":7,\"\"length\"\":25},\"\"policyEntity\"\":{\"\"parameters\"\":[{\"\"name\"\":\"\"*\"\",\"\"level\"\":\"\"global\"\",\"\"type\"\":\"\"wildcard\"\"}]},\"\"observedEntity\"\":{\"\"name\"\":\"\"c3Zhbmdh\"\",\"\"value\"\":\"\"PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0PiI=\"\",\"\"location\"\":\"\"query\"\"}}],\"\"enforcementAction\"\":\"\"block\"\",\"\"method\"\":\"\"GET\"\",\"\"clientPort\"\":64344,\"\"clientIp\"\":\"\"128.175.220.223\"\",\"\"host\"\":\"\"nginxplus-nginx-ingress-controller-6498464cd4-k57b5\"\",\"\"responseCode\"\":0,\"\"serverIp\"\":\"\"0.0.0.0\"\",\"\"serverPort\"\":443,\"\"requestStatus\"\":\"\"blocked\"\",\"\"url\"\":\"\"L3dhZg==\"\",\"\"virtualServerName\"\":\"\"14-cyberwasp-sv-helloworld.ikp3001ynp.cloud.uk.fed:24-/waf\"\",\"\"geolocationCountryCode\"\":\"\"US\"\",\"\"enforcementState\"\":{\"\"isBlocked\"\":true,\"\"isAlarmed\"\":true,\"\"rating\"\":5,\"\"attackType\"\":[{\"\"name\"\":\"\"Cross Site Scripting (XSS)\"\"}],\"\"ratingIncludingViolationsInStaging\"\":5,\"\"stagingCertificationDatetime\"\":\"\"1970-01-01T00:00:00Z\"\"},\"\"requestDatetime\"\":\"\"2025-06-26T13:40:31Z\"\",\"\"rawRequest\"\":{\"\"actualSize\"\":1016,\"\"httpRequest\"\":\"\"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\"\",\"\"isTruncated\"\":false},\"\"requestPolicy\"\":{\"\"fullPath\"\":\"\"waf-fed-enforced\"\"}}\",violation_details=\"<?xml version='1.0' encoding='UTF-8'?>\n" "<BAD_MSG>\n" "<violation_masks>\n" "<block>400500200500-1a01030000000032-0-0</block>\n" "<alarm>20400500200500-1ef903400000003e-7400000000000000-0</alarm>\n" "<learn>0-0-0-0</learn>\n" "<staging>0-0-0-0</staging>\n" "</violation_masks>\n" "<request-violations>\n" "<violation>\n" "<viol_index>42</viol_index>\n" "<viol_name>VIOL_ATTACK_SIGNATURE</viol_name>\n" "<context>parameter</context>\n" "<parameter_data>\n" "<value_error/>\n" "<enforcement_level>global</enforcement_level>\n" "<name>c3Zhbmdh</name>\n" "<value>PHNjcmlwdD5hbGVydCgxKTwvc2NyaXB0PiI=</value>\n" "<location>query</location>\n" "<expected_location>\n" "</expected_location>\n" "<is_base64_decoded>false</is_base64_decoded>\n" "<param_name_pattern>*</param_name_pattern>\n" "<staging>0</staging>\n" "</parameter_data>\n" "<staging>0</staging>\n" "<sig_data>\n" "<sig_id>200001475</sig_id>\n" "<blocking_mask>3</blocking_mask>\n" "<kw_data>\n" "<buffer>c3ZhbmdhPTxzY3JpcHQ+YWxlcnQoMSk8L3NjcmlwdD4i</buffer>\n" "<offset>8</offset>\n" "<length>7</length>\n" "</kw_data>\n" "</sig_data>\n" "<sig_data>\n" "<sig_id>200000098</sig_id>\n" "<blocking_mask>3</blocking_mask>\n" "<kw_data>\n" "<buffer>c3ZhbmdhPTxzY3JpcHQ+YWxlcnQoMSk8L3NjcmlwdD4i</buffer>\n" "<offset>7</offset>\n" "<length>7</length>\n" "</kw_data>\n" "</sig_data>\n" "<sig_data>\n" "<sig_id>200001088</sig_id>\n" "<blocking_mask>2</blocking_mask>\n" "<kw_data>\n" "<buffer>c3ZhbmdhPTxzY3JpcHQ+YWxlcnQoMSk8L3NjcmlwdD4i</buffer>\n" "<offset>15</offset>\n" "<length>6</length>\n" "</kw_data>\n" "</sig_data>\n" "<sig_data>\n" "<sig_id>200101609</sig_id>\n" "<blocking_mask>3</blocking_mask>\n" "<kw_data>\n" "<buffer>c3ZhbmdhPTxzY3JpcHQ+YWxlcnQoMSk8L3NjcmlwdD4i</buffer>\n" "<offset>7</offset>\n" "<length>25</length>\n" "</kw_data>\n" "</sig_data>\n" "</violation>\n" "</request-violations>\n" "</BAD_MSG>\",bot_signature_name=\"N/A\",bot_category=\"N/A\",bot_anomalies=\"N/A\",enforced_bot_anomalies=\"N/A\",client_class=\"Browser\",client_application=\"Chrome\",client_application_version=\"133\",request=\"GET /waf?svanga=%3Cscript%3Ealert(1)%3C/script%3E%22 HTTP/1.1\\r\\nhost: cyberwasp-sv-helloworld.ikp3001ynp.cloud.uk.fed\\r\\ncache-control: max-age=0\\r\\nsec-ch-ua: \"\"Not(A:Brand\"\";v=\"\"99\"\", \"\"Google Chrome\"\";v=\"\"133\"\", \"\"Chromium\"\";v=\"\"133\"\"\\r\\nsec-ch-ua-mobile: ?0\\r\\nsec-ch-ua-platform: \"\"Windows\"\"\\r\\nupgrade-insecure-requests: 1\\r\\nuser-agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/133.0.0.0 Safari/537.36\\r\\naccept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7\\r\\nsec-fetch-site: none\\r\\nsec-fetch-mode: navigate\\r\\nsec-fetch-user: ?1\\r\\nsec-fetch-dest: document\\r\\naccept-encoding: gzip, deflate, br, zstd\\r\\naccept-language: en-US,en;q=0.9\\r\\npriority: u=0, i\\r\\ncookie: ajs_user_id=58a7143edf3a5119b80c3c453acbdc1655a0a79a; ajs_anonymous_id=ce332d12-b974-49e2-b93c-15eab5fba064; amp_33557d=mrNI_Ya3kZXwACmcPaSlxG...1inejviav.1inekn40u.0.0.0; amp_33557d_uk.fed=mrNI_Ya3kZXwACmcPaSlxG...1inejvib3.1inekn411.0.0.0\\r\\n\\r\\n\",transport_protocol=\"HTTP/2.0\"") 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