Match multiline text using regular expression

Question

I am trying to match a multi line text using java  When I use the Pattern class with the Pattern MULTILINE modifier  I am able to match  but I am not able to do so with   m    The same pattern with   m  and using String matches does not seem to work   I am sure I am missing something  but no idea what  Am not very good at regular expressions   This is what I tried  String test    User Comments  This is  t a ta  n test  n n message  n    String pattern1    User Comments     W     S     Pattern p   Pattern compile pattern1  Pattern MULTILINE   System out println p matcher test  find        true  String pattern2      m User Comments     W     S     System out println test matches pattern2       false - why

User · Answer

The multiline flag tells regex to match the pattern to each line as opposed to the entire string for your purposes a wild card will suffice

User · Answer

This has nothing to do with the MULTILINE flag  what you re seeing is the difference between the find   and matches   methods   find   succeeds if a match can be found anywhere in the target string  while matches   expects the regex to match the entire string   Pattern p   Pattern compile  xyz     Matcher m   p matcher  123xyzabc    System out println m find           true System out println m matches        false  Matcher m   p matcher  xyz    System out println m matches        true   Furthermore  MULTILINE doesn t mean what you think it does   Many people seem to jump to the conclusion that you have to use that flag if your target string contains newlines--that is  if it contains multiple logical lines   I ve seen several answers here on SO to that effect  but in fact  all that flag does is change the behavior of the anchors    and       Normally   matches the very beginning of the target string  and   matches the very end  or before a newline at the end  but we ll leave that aside for now    But if the string contains newlines  you can choose for   and   to match at the start and end of any logical line  not just the start and end of the whole string  by setting the MULTILINE flag   So forget about what MULTILINE means and just remember what it does  changes the behavior of the   and   anchors   DOTALL mode was originally called  single-line   and still is in some flavors  including Perl and  NET   and it has always caused similar confusion   We re fortunate that the Java devs went with the more descriptive name in that case  but there was no reasonable alternative for  multiline  mode     In Perl  where all this madness started  they ve admitted their mistake and gotten rid of both  multiline  and  single-line  modes in Perl 6 regexes   In another twenty years  maybe the rest of the world will have followed suit

User · Answer

str matches regex  behaves like Pattern matches regex   str  which attempts to match the entire input sequence against the pattern and returns     true if  and only if  the entire input sequence matches this matcher s pattern   Whereas matcher find   attempts to find the next subsequence of the input sequence that matches the pattern and returns      true if  and only if  a subsequence of the input sequence matches this matcher s pattern   Thus the problem is with the regex  Try the following   String test    User Comments  This is  t a ta  ntest n n message  n    String pattern1    User Comments     s  S   test    s  S     Pattern p   Pattern compile pattern1  Pattern MULTILINE   System out println p matcher test  find        true  String pattern2      m User Comments     s  S   test    s  S     System out println test matches pattern2       true   Thus in short  the    W     S   portion in your first regex matches an empty string as   means zero or more occurrences and the real matched string is User Comments  and not the whole string as you d expect  The second one fails as it tries to match the whole string but it can t as   W matches a non word character  ie   a-zA-Z0-9   and the first character is T  a word character

User · Answer

First  you re using the modifiers under an incorrect assumption   Pattern MULTILINE or   m  tells Java to accept the anchors   and   to match at the start and end of each line  otherwise they only match at the start end of the entire string    Pattern DOTALL or   s  tells Java to allow the dot to match newline characters  too   Second  in your case  the regex fails because you re using the matches   method which expects the regex to match the entire string - which of course doesn t work since there are some characters left after    W     S   have matched   So if you re simply looking for a string that starts with User Comments   use the regex    s User Comments  s        with the Pattern DOTALL option   Pattern regex   Pattern compile     s User Comments   s        Pattern DOTALL   Matcher regexMatcher   regex matcher subjectString   if  regexMatcher find          ResultString   regexMatcher group 1        ResultString will then contain the text after User Comments

[java] Match multiline text using regular expression

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