Re: About regular expression

Hello

I'll try explaining what this code does. But first: about regular expressions.

Without getting too technical, Regular Expressions are one way of describing a set of words. So, when we say

if ($str =~ /some_re/){
  do something ...
}
[download]

what we're really doing is asking if the string belongs to the set described by the regular expression.

I don't (and can't) explain the whole of perl's regular expressions but I'll explain enough to make you understand the code segment.

```
/A/
```
describes all words that contain the capital letter A.
```
/abc/
```
describes all words that contain the sequence 'abc' ("abc", "sjdhabcsd", aaabc", ...).
```
/^abc/
```
describes all words that begin with the sequence "abc" ("abc", "abcdefg", "abcccccc").
```
/abc$/
```
describes all words that end with the sequence "abc" ("abc", "sjdhjabc", "aaabc").
```
/a*/
```
describes all words that have zero or more of the letter 'a' ("", "abcj", or anything really).
```
/(ab)*/
```
describes all words that have zero or more of the sequence 'ab' ("", "ab", "abab", "cdr", "tryabtry", ...).
```
/[abc]/
```
contains any of 'a', 'b', or 'c'.
```
/[^abc]/
```
none of these: for example
```
/a[^bc]d/
```
means 'a' followed by anything but 'b' or 'c', followed by a 'd'.
```
/./
```
matches anything so
```
/a.c/
```
describes all words than contain 'a' followed by anything, followed by a 'c' ("aac", "abc", "a c", ...). To match a dot '.', you need to escape it with a \.

foreach (qw/one one.five two two.one two.ten 
            two.ten.12 three three.nine four five/){
   print "$_\n";
   if($_ =~ /\./){ # if the word has a dot ".".
      # Keep everything after the last "." in the string   
      my ($label) = /\.([^\.]*)$/;    # a dot, followed by zero 
                                   # or more letters that are
                                   # not dots, attached to the 
                                   # end of the string.
                                   # return those letters
                                   # since they're between 
                                   # brackets.    
      $tree->add($_, -text  => $label , # add the label to $tree
                     -image => $mw->Getimage(folder));
   }
}
[download]

Hope this helped

Aziz,,,

Update: Thanks blakem for pointing out the need for escapes for \] in <pre> tags.

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