Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I was hoping someone could tell me what this is doing in as much detail as you can?? 
unless $target =~ /^(?:https?|ftp):/;

[download]

Replies are listed 'Best First'.
Re: Need interpretation of line
by davorg (Chancellor) on Sep 19, 2002 at 10:39 UTC

    It checks to see if $target starts with 'http', 'https' or 'ftp', followed by ':'.

    --
    <http://www.dave.org.uk>

    "The first rule of Perl club is you do not talk about Perl club."
    -- Chip Salzenberg

[reply]
      thank you for your quick answer. So the unless part is saying if $target does not start with 'http', 'https' or 'ftp', followed by a '.'?
[reply]

        That's right.

        --
        <http://www.dave.org.uk>

        "The first rule of Perl club is you do not talk about Perl club."
        -- Chip Salzenberg

[reply]
Re: Need interpretation of line
by flounder99 (Friar) on Sep 19, 2002 at 14:03 UTC
    A handy tool for understanding complex regexes is YAPE::Regex::Explain 
    $ perl -e 'use YAPE::Regex::Explain;print YAPE::Regex::Explain->new("^
+(?:https?|ftp):")->explain;'
The regular expression:

(?-imsx:^(?:https?|ftp):)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?-imsx:                 group, but do not capture (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n) (matching whitespace and #
                         normally):
----------------------------------------------------------------------
  ^                        the beginning of the string
----------------------------------------------------------------------
  (?:                      group, but do not capture:
----------------------------------------------------------------------
    http                     'http'
----------------------------------------------------------------------
    s?                       's' (optional (matching the most amount
                             possible))
----------------------------------------------------------------------
   |                        OR
----------------------------------------------------------------------
    ftp                      'ftp'
----------------------------------------------------------------------
  )                        end of grouping
----------------------------------------------------------------------
  :                        ':'
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

    [download]

    --

    flounder

[reply]
[d/l]
[select]

Back to Seekers of Perl Wisdom