Newsgroups: comp.lang.perl
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!convex!usenet
From: Tom Christiansen <tchrist@convex.COM>
Subject: Re: tr doesn't count
Message-ID: <1991Jun25.181707.7846@convex.com>
Sender: usenet@convex.com (news access account)
Nntp-Posting-Host: pixel.convex.com
Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
References: <cluther.677868757@sonne>
Date: Tue, 25 Jun 1991 18:17:07 GMT
Lines: 47

From the keyboard of cluther@sonne.cnns.unt.edu (Clay Luther):
:Given,
:
:$c = "3/3/3";
:$c = tr/\//\//;
:
:Why is $c set to 0 and not 2?

Because $_ (the default operand for the tr/// operator) 
doesn't have any slashes in it.  If you had done this:

    $_ = "3/3/3";
    $c = tr/\//\//;

It would have done what you wer expecting.  Try this:


    $string = "3/3/3";

then

    $count = ( $string =~ tr#/#/#; );

which is the same as: 

    $count = $string =~ tr#/#/#;;

but since I'm never 100.000000000% sure it's not 

    ($count = $string) =~ tr#/#/#;

I use the parens anyway.

With recent patches, you could also use this:
    
    $count++ while $string =~ m#/#g;

Although the tr/// runs a good deal faster.  40% the time
for m//g in this case, even better with more things to
match.  I guess the moral is for counting single chars, use
tr///, but for counting longer patterns, you'll need m//g.


--tom
--
Tom Christiansen		tchrist@convex.com	convex!tchrist
		"So much mail, so little time."