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

Substitution

Processing...

Code Generator

Language

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "\\$([^\\{(\"\\\\'\\/])([a-zA-Z0-9_]*)([^\\}\\/ \\t'\"\\n.\\]:]*)"; final String string = "#!/usr/bin/env bash\n\n" + "# version 0.1.0\n\n" + "function generate_secret()\n" + "{\n" + " ( umask 0077 ; dd if=/dev/urandom bs=24 count=1 2>/dev/null | base64 -w0 > \"$1\" )\n" + "}\n\n" + "if [[ -n $SRS_DOMAINNAME ]]\n" + "then\n" + " NEW_DOMAIN_NAME=\"$SRS_DOMAINNAME\"\n" + "elif [[ -n $OVERRIDE_HOSTNAME ]]\n" + "then\n" + " NEW_DOMAIN_NAME=\"${OVERRIDE_HOSTNAME#*.}\"\n" + "elif [[ -n $DOMAINNAME ]]\n" + "then\n" + " NEW_DOMAIN_NAME=\"$DOMAINNAME\"\n" + "else\n" + " NEW_DOMAIN_NAME=$(hostname -d)\n" + "fi\n\n" + "sed -i -e \"s/localdomain/${NEW_DOMAIN_NAME}/g\" /etc/default/postsrsd\n\n" + "POSTSRSD_SECRET_FILE='/etc/postsrsd.secret'\n" + "POSTSRSD_STATE_DIR='/var/mail-state/etc-postsrsd'\n" + "POSTSRSD_STATE_SECRET_FILE=\"${POSTSRSD_STATE_DIR}/postsrsd.secret\"\n\n" + "if [[ -n $SRS_SECRET ]]\n" + "then\n" + " ( umask 0077 ; echo \"$SRS_SECRET\" | tr ',' '\\n' > \"$POSTSRSD_SECRET_FILE\" )\n" + "else\n" + " if [[ $ONE_DIR -eq 1 ]]\n" + " then\n" + " if [[ ! -f $POSTSRSD_STATE_SECRET_FILE ]]\n" + " then\n" + " install -d -m 0775 \"$POSTSRSD_STATE_DIR\"\n" + " generate_secret \"$POSTSRSD_STATE_SECRET_FILE\"\n" + " fi\n\n" + " install -m 0400 \"$POSTSRSD_STATE_SECRET_FILE\" \"$POSTSRSD_SECRET_FILE\"\n" + " elif [[ ! -f $POSTSRSD_SECRET_FILE ]]\n" + " then\n" + " generate_secret \"$POSTSRSD_SECRET_FILE\"\n" + " fi\n" + "fi\n\n" + "if [[ -n $SRS_EXCLUDE_DOMAINS ]]\n" + "then\n" + " sed -i -e \"s/^#\\?SRS_EXCLUDE_DOMAINS=.*$/SRS_EXCLUDE_DOMAINS=$SRS_EXCLUDE_DOMAINS/g\" /etc/default/postsrsd\n" + "fi\n\n" + "/etc/init.d/postsrsd start\n"; final String subst = "${$1$2$3}"; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE); final Matcher matcher = pattern.matcher(string); // The substituted value will be contained in the result variable final String result = matcher.replaceAll(subst); System.out.println("Substitution result: " + result); } }

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 Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html