in reply to quite weird regexp

You can use any non-alphanumeric character as the separator in a s/// or m// operator. This allows you to choose a separator which doesn't clash with the data in the string.

In this case, if you used the 'traditional' slash as the delimiter then you'd need to escape the slash that appears in the regex. By changing the separator, you don't need to do that.

You can also use 'bracketing' characters, like (, [, < or {. In that case you need to use the opposite character at the other end, like this:

s[something][else];

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This is all explained in perldoc perlop.

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

"Perl makes the fun jobs fun
and the boring jobs bearable" - me

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Re: Re: quite weird regexp
by chipmunk (Parson) on Nov 30, 2000 at 19:33 UTC
    What perlop doesn't tell you is that, if you put a space after the operator name, you can use alphanumeric characters as delimiters. To use the current example: ($Z = $0) =~ s z.*/zz; I also made use of this in homer.pl, with m mmm, Donuts. But please don't do this in production code! :)
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Re: Re: quite weird regexp
by clemburg (Curate) on Nov 30, 2000 at 19:45 UTC

    To be precise (citing from perlop manpage):

    • Whitespace is not a valid delimiter, and there are additional semantics associated with single quotes: 
      s/PATTERN/REPLACEMENT/egimosx
 
 [ ... snip ...]

               Any non-alphanumeric, non-whitespace delimiter may
               replace the slashes.  If single quotes are used,
               no interpretation is done on the replacement
               string (the /e modifier overrides this, however).
               Unlike Perl 4, Perl 5 treats backticks as normal
               delimiters; the replacement text is not evaluated
               as a command.  If the PATTERN is delimited by
               bracketing quotes, the REPLACEMENT has its own
               pair of quotes, which may or may not be bracketing
               quotes, e.g., s(foo)(bar) or s<foo>/bar/.  A /e
               will cause the replacement portion to be
               interpreted as a full-fledged Perl expression and
               eval()ed right then and there.  It is, however,
               syntax checked at compile-time.

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    • with m//, you also want to watch out not to use '?' as the delimiter, as this has a different meaning: 
         ?PATTERN?
               This is just like the /pattern/ search, except
               that it matches only once between calls to the
               reset() operator.  This is a useful optimization
               when you want to see only the first occurrence of
               something in each file of a set of files, for
               instance.  Only ??  patterns local to the current
               package are reset.

[ ... snip ...]

       m/PATTERN/cgimosx

       /PATTERN/cgimosx

[ ... snip ...]

               If "/" is the delimiter then the initial m is
               optional.  With the m you can use any pair of non-
               alphanumeric, non-whitespace characters as
               delimiters. This is particularly useful for
               matching Unix path names that contain "/", to
               avoid LTS (leaning toothpick syndrome). If "?" is
               the delimiter, then the match-only-once rule of
               ?PATTERN? applies.  If "'" is the delimiter, no
               variable interpolation is performed on the
               PATTERN.

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      This is all explained in perldoc perlop (there is no "perlops" manpage).

      Christian Lemburg
      Brainbench MVP for Perl
      http://www.brainbench.com

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RTF(antastic)M (Re: Re: quite weird regexp)
by larsen (Parson) on Nov 30, 2000 at 15:14 UTC
    Thank you very much.
    (Alas, perhaps I count from 1 to 10 too quickly :) )
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