List of all special characters that need to be escaped in a regex

Question

I am trying to create an application that matches a message template with a message that a user is trying to send  I am using Java regex for matching the message  The template message may contain special characters   How would I get the complete list of special characters that need to be escaped in order for my regex to work and match in the maximum possible cases   Is there a universal solution for escaping all special characters in Java regex

User · Answer

Combining what everyone said  I propose the following  to keep the list of characters special to RegExp clearly listed in their own String  and to avoid having to try to visually parse thousands of      s   This seems to work pretty well for me   final String regExSpecialChars     lt       -            gt    final String regExSpecialCharsRE   regExSpecialChars replaceAll             0    final Pattern reCharsREP   Pattern compile        regExSpecialCharsRE          String quoteRegExSpecialChars  String s        Matcher m   reCharsREP matcher  s       return m replaceAll        0

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Assuming that you have and trust  to be authoritative  the list of escape characters Java regex uses  would be nice if these characters were exposed in some Pattern class member  you can use the following method to escape the character if it is indeed necessary   private static final char   escapeChars       lt                               -                                                            gt       private static String regexEscape char character        for  char escapeChar   escapeChars            if  character    escapeChar                return        character                      return String valueOf character

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To escape you could just use this from Java 1 5   Pattern quote   test      You will match exacty the word  test

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Java characters that have to be escaped in regular expressions are           lt  gt   -       Two of the closing brackets    and    are only need to be escaped after opening the same type of bracket  In   -brackets some characters  like   and -  do sometimes work without escape

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although the answer is for Java  but the code can be easily adapted from this Kotlin String extension I came up with  adapted from that  brcolow provided    private val escapeChars   charArrayOf        lt                                                       -                                                                                                            gt      fun String escapePattern    String       return this fold             acc  chr - gt          acc   if  escapeChars contains chr       chr  else   chr           fun main         println        escapePattern        prints           check it in action here https   pl kotl in h-3mXZkNE

User · Answer

The Pattern quote String s  sort of does what you want  However it leaves a little left to be desired  it doesn t actually escape the individual characters  just wraps the string with  Q    E    There is not a method that does exactly what you are looking for  but the good news is that it is actually fairly simple to escape all of the special characters in a Java regular expression   regex replaceAll     W          0     Why does this work  Well  the documentation for Pattern specifically says that its permissible to escape non-alphabetic characters that don t necessarily have to be escaped      It is an error to use a backslash prior to any alphabetic character that does not denote an escaped construct  these are reserved for future extensions to the regular-expression language  A backslash may be used prior to a non-alphabetic character regardless of whether that character is part of an unescaped construct     For example    is not a special character in a regular expression  However  if you escape it  Pattern will still interpret    as    Here are a few more examples     gt  becomes   gt  which is equivalent to  gt    becomes    which is the escaped form of   8 is still 8     becomes      which is the escaped forms of   and   concatenated     Note  The key is is the definition of  non-alphabetic   which in the documentation really means  non-word  characters  or characters outside the character set  a-zA-Z 0-9

User · Answer

On  Sorin s suggestion of the Java Pattern docs  it looks like chars to escape are at least

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According to the String Literals   Metacharacters documentation page  they are    lt      -            gt   Also it would be cool to have that list refereed somewhere in code  but I don t know where that could be

User · Answer

on the other side of the coin  you should use  non-char  regex that looks like this if special characters   allChars - number - ABC - space in your app context   String regepx        s  w

User · Answer

You can look at the javadoc of the Pattern class  http   docs oracle com javase 8 docs api java util regex Pattern html  You need to escape any char listed there if you want the regular char and not the special meaning   As a maybe simpler solution  you can put the template between  Q and  E - everything between them is considered as escaped

[java] List of all special characters that need to be escaped in a regex

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