Perl regex (Regular expressions) examples

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Perl Regular Expressions

Metacharacters

char meaning
^      beginning of string 
$      end of string 
.      any character except newline 
*      match 0 or more times 
+      match 1 or more times 
?      match 0 or 1 times; or: shortest match 
|      alternative 
( )    grouping; "storing" 
[ ]    set of characters 
{ }    repetition modifier 
\      quote or special

Repetition
a*     zero or more a's 
a+     one or more a's 
a?     zero or one a's (i.e., optional a) 
a{m}   exactly m a's 
a{m,}  at least m a's 
a{m,n} at least m but at most n a's repetition?
 
\t     tab 
\n     newline 
\r     return (CR) 
\xhh   character with hex. code hh 
\b     "word" boundary 
\B     not a "word" boundary 

\w     matches any single character classified as a 
       "word" character (alphanumeric or _) 
\W     matches any non-"word" character 
\s     matches any whitespace character (space, tab, newline) 
\S     matches any non-whitespace character  
\d     matches any digit character, equiv. to [0-9] 
\D     matches any non-digit character 

[characters] matches any of the characters in the sequence  
[x-y]        matches any of the characters from x to y 
             (inclusively) in the ASCII code  
[\-]         matches the hyphen character - 
[\n]         matches the newline; other single character 
             denotations with  apply normally, too

Examples How do I extract everything between a the words "start" and "end"?
$mystring = "The start text always precedes the end of the end text.";
if($mystring =~ m/start(.*)end/) {
print $1;
}

How do I extract a complete number, like the year?
$mystring = "[2004/04/13] The date of this article.";
if($mystring =~ m/(d+)/) {
print "The first number is $1.";
}

# find word that is bolded
# returns: $1 = 'text'
$line = "This is some text with HTML and ";
$line =~ m/(.*)/i;