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

r"
"
xmg

Test String

Code Generator

Language

Generated Code

use strict; my $str = '5. What ultrasound finding in a breast lesion is typically associated with malignancy? A. Increased through transmission B. Height greater than width C. Hyperechogenicity D. Surrounding hyperechoic halo Key: B Rationale: A. Incorrect. Increased through transmission is typically associated with benign simple cysts. B. Correct. Height greater than width is a sonographic feature that is typically associated with malignancy. C. Incorrect. Hyperechogenicity typically is seen with benign fat containing lesions and is not a typical feature of malignancy. D. Incorrect. A surrounding hyperechoic (echogenic) halo is typically associated with benign post traumatic findings. References: Stavros AT. Breast Ultrasound. Lippincott Williams and Wilkins, 2004. P. 472. 6. For which ONE of the following would a BIRADS 6 classification be MOST appropriate? A. Post procedure mammogram for marker placement B. Prior treated breast cancer C. Recent biopsy proven breast cancer D. Suspicious abnormality; needs biopsy Key: C Rationale: A. Incorrect. A Birads category is not given on the post procedure mammogram for marker placement. B. Incorrect. Patients with a history of breast cancer are not assigned a Birads Category 6, which is reserved for patients with known (untreated as yet) malignancy. C. Correct. Birads Category 6 is assigned to patients with a diagnosis of cancer who have not yet been definitively treated. D. Incorrect. Patients with suspicious abnormalities; need biopsy should be coded Birads Category 4. Birads 6 is reserved for patients with a known biopsy proven diagnosis of breast cancer. References: ACR BIRADS Atlas, 5th Edition, 2013. P. 149-159.'; my $regex = qr/(?ms)^\d+\.\s*(.*?)(?=^\d+\.|\Z)/xmp; if ( $str =~ /$regex/g ) { print "Whole match is ${^MATCH} and its start/end positions can be obtained via \$-[0] and \$+[0]\n"; # print "Capture Group 1 is $1 and its start/end positions can be obtained via \$-[1] and \$+[1]\n"; # print "Capture Group 2 is $2 ... and so on\n"; } # ${^POSTMATCH} and ${^PREMATCH} are also available with the use of '/p' # Named capture groups can be called via $+{name}

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 Perl, please visit: http://perldoc.perl.org/perlre.html