Fell off the Llama

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

Hey Folks,

I see that my former posts have been moded up to where I am now a "monk". While I appreciate the honor, I have to say that I am truly not worthy of that title. I am a seeker, not a dispenser of perl wisdom. I will dispense once I've learned enough. So please mod away! ...down! :D

Well, it's true. Sadly, I have fallen off the Llama. In the past 3 weeks, I've had two valued family members die on me, had my place vandalized (on the day she dies with all kinds of ritualistic santa rea strangeness) and had a terrible session with my therapist.

But, sadly now that I am climbing back on the Llama I find that a lot of Perl knowledge has just sort of drained out of my mind. I am bummed. I want to get back to where I was and continue improving.

For some reason, my brain is so addled that I can't seem to make heads or tales of chp 9 ex 1 *OR* it's answer in the back of the book! god help me! :)

The question states that you should "Make a pattern that will match three consecutive copies of whatever is currently contained in $what. That is, if $what is fred, your pattern should match fredfredfred. If $what is fred|barney, your pattern should match fredfredbarney or barneyfredfred or barneybarneybarney or many other variations. (Hint: You should set $what at the top of the pattern test program with a statement like my $what = 'fred|barney' ;.)

The answer says here's one way to do it:

/(what) {3}/

Once $what has been interpolated, this gives a pattern resembling /(fred|barney){3}/. Without the parenthesis, the pattern would be something like /fred|barney{3}/, which is the same /fred|barneyyy/. So, the parenthesis are required.

Sorry for being so obtuse, but I can't seem to make heads or tales of this problem *OR* it's answer! You thoughts and comments would be appreciated!

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Re: Fell off the Llama by Roy Johnson (Monsignor) on Jun 24, 2004 at 18:40 UTC
It can be hard to focus on things when you've been through a lot of emotional events, so you might just need a little more time before you climb back on. But if you feel like you're really ready, here's as good a job as I can do to make the exercise even more clear. The exercise is dealing with regular expressions (which the book is calling patterns), which are a kind of string-description language. The Perl operator for applying a regular expression to a string to see if it matches, is the "match operator", m//. The m is optional (and generally omitted) if slashes are used. The regular expression goes between the slashes. To see if `$_` matches `$pattern`, we just do `/$pattern/`. To see if the pattern in `$what` appears somewhere in `$_` three times in a row, we can do `/$what$what$what/`, or `/($what){3}/` for short. We're not really tightening our belts, it just feels that way because we're getting fatter.	[reply] [d/l] [select]
Re^2: Fell off the Llama by ysth (Canon) on Jun 25, 2004 at 05:02 UTC
The parentheses are just as necessary without the {} construct. If $what is 'fred\|barney', you want to match `/(fred\|barney)(fred\|barney)(fred\|barney)/`, not `/fred\|barneyfred\|barneyfred\|barney/`. I see from fred that fred and barney are fully paid up members of the metasyntactic variable club :)	[reply] [d/l] [select]
Re: Fell off the Llama by theorbtwo (Prior) on Jun 24, 2004 at 18:01 UTC
It would appear that there is an error in the provided answer; it should be `/($what){3}/`. Warning: Unless otherwise stated, code is untested. Do not use without understanding. Code is posted in the hopes it is useful, but without warranty. All copyrights are relinquished into the public domain unless otherwise stated. I am not an angel. I am capable of error, and err on a fairly regular basis. If I made a mistake, please let me know (such as by replying to this node).	[reply] [d/l]
•Re^2: Fell off the Llama by merlyn (Sage) on Jun 24, 2004 at 19:18 UTC
The Book absolutely has `/($what){3}/` [download] The OP quoted it wrong. -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply.	[reply] [d/l]
Re^2: Fell off the Llama by Fletch (Bishop) on Jun 24, 2004 at 18:21 UTC
ORA's usually pretty good about maintaining errata for their titles. I don't see this particular typo listed, so the original poster might want to use the submit link on that page and let them know (presuming it's the 3rd edition we're talking about; I didn't check the errata for the prior editions).	[reply]
Re: Fell off the Llama by pbeckingham (Parson) on Jun 24, 2004 at 19:06 UTC
The stated answer includes a space between the right paren and the brace, which means that it won't work unless the `x` is added, like: `/(what) {3}/x` [download] Deleting the space will also work: `/(what){3}/` [download] But it does capture, and it doesn't have to if that is not what's needed - just use non-capturing grouping: `/(?:what){3}/` [download]	[reply] [d/l] [select]
Re^2: Fell off the Llama by theorbtwo (Prior) on Jun 25, 2004 at 01:43 UTC
Your answer doesn't quite match the question: "Make a pattern that will match three consecutive copies of whatever is currently contained in $what." Your solution fails to match what is contained in $what; it mearly matches the string 'what'. Warning: Unless otherwise stated, code is untested. Do not use without understanding. Code is posted in the hopes it is useful, but without warranty. All copyrights are relinquished into the public domain unless otherwise stated. I am not an angel. I am capable of error, and err on a fairly regular basis. If I made a mistake, please let me know (such as by replying to this node).	[reply]
Re: Fell off the Llama by ysth (Canon) on Jun 25, 2004 at 05:09 UTC
I am now a "monk". While I appreciate the honor, I have to say that I am truly not worthy of that title. I am a seeker, not a dispenser of perl wisdom. Seekers are also worthy of advancement through the ranks. See Sainthood via Seniority Simulation.	[reply]
Re: Fell off the Llama by talexb (Chancellor) on Jun 25, 2004 at 16:33 UTC
My sympathies on your recent bout of bad fortune. Perhaps now is a bad time to try and wrap your head around OO concepts -- I wouldn't work too hard on that right now, rather, I'd probably take some time off. Put the brain in neutral, relax, go for long walks, sleep in, let the body and the mind heal. You'll know how long that period needs to be -- then you can dive into the Llama again. Good luck! Alex / talexb / Toronto Life is short: get busy!	[reply]