Regex Tutorial - Metacharacter "{}" in Regular Expression.

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Regular-expression

Topic

Whats the use of "{}" metacharacter?

Explanation

The "{}" braces metacharacter otherwise known as quantifiers is used to specify the range for matching the patterns.

Metacharacter	Description
{n}	Match n times
{n,}	Match n or more times
{m,n}	Match atleast m times,and utmost n times

The pattern "o{3}l" will match strings like "loool", "oool", "llloool" as all the strings have only three o's followed by an "l".If the pattern "o{3,}l" it will match the strings like "ooooooool", "looooool" etc. Exactly a range can be given using the pattern "o{2,4}l" will match the strings like "lool","loool","looool" etc.

To match a sequence of characters, try a pattern "o(lu)*" where it matches a "o" followed by zero or more occurences of the pattern "lu", the matches can be "o","olu", "olulu" etc. Same pattern can also be given within a range like "o(lu){1,2}" possible matches would be "o","olu","olulu" only.

PHP Example:

    <?php
    $name = "live1";
    if (preg_match("/^.{2,4}$/", $name))
     { echo "Pattern matches!";} 
    else 
     { echo "Pattern not matched!";}
    ?>

Result:

    Pattern not matched!

In the above example the pattern "/^.{2,4}$/" this matches any string with 2 to 4 characters, since "live1" has five character's it is not matched, but if changed to "live" it can be a matched.

Perl Example:

    #! C:\programfiles\perl\bin\perl
    print "content-type: text/html\n\n";
    if ("oooool" =~ m/o{2,4}l/) 
      {print "The pattern matched.!\n";} 
    else 
      { print "The pattern not matched!\n"; }

Result:

    The pattern matched!

In the above example's the pattern "o{2,4}l" means the string should have atleat 2 to 4 "o"s followed by "l", since that string "oooool" has 5 o's, followed by a "l", the pattern is matched because the exceeding range is negelected after the match.

How to use "{}" metacharacter in Regular Expression.