in reply to while loop logic

As soon as I saw a label (LOOP:) in your code, I knew we were in for something confusing. Sure enough, a couple of lines later, there's a next, but it's not just a plain next; it has to use the label, because the are intervening control-flow structures. The while loop logic in itself is not your problem. It's the logic of next that gets things all confused, and then to make it even more confusing you slap an until on the next. That's at least three levels of control-flow structures involved, which IMO is too many. (The amount of confusion surrounding next increases geometrically with the amount of control-flow structure involved.) I'm sure someone here is clever enough to iron out exactly how to make next skip the desired iterations, but I'm even more sure that there are less confusing ways to achieve what you want.

Others have suggested only printing if you aren't inside a comment. That'll work fine, and is a good way to do it. In the interest of of TMTOWTDI, another solution would be to do something like this when you detect the beginning of a comment:

  { local $/ = '*/'; <CMDTXTF>; } <CMDTXTF>;

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The first diamond operator slurps everything up to the close of the comment in one fell swoop. The localized $/ tells it how far to go. The braces keep the change in $/ from leaking out to spoil the rest of your code. The second diamond operator should clean up the rest of the line after the */, even if it's just a newline character, so that you're ready for the next line when the loop resumes.

One caveat: if any of the lines might have $/ in other fields besides the fifth one, which don't apply to the fifth field (e.g., perhaps the fourth field of several consecutive records is commented out in this fashion, with no implications for the fifth), then this solution isn't smart enough to deal with that correctly.

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Re^2: while loop logic
by Anonymous Monk on Jan 13, 2006 at 15:19 UTC
    I am intrigued by this answer. Being fairly new to Perl this has opened up a new ball game for me. I have a further question based on the answer you've given.
    What happens if all I want to do is to chop out the comment from the fifth field (which is the only one that will ever contain comments) but apply the regex to what remains of the field? e.g. 

    aaaa|bbbb|cccc|dddd|eeee|some text to check /* a comment
qqqq|wwww|eeee|rrrr|tttt| I'm not interested in */ more text to check

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    Can I do this using your solution ?
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[d/l]
      What happens if all I want to do is to chop out the comment from the fifth field (which is the only one that will ever contain comments) but apply the regex to what remains of the field?

      Potentially, if you don't care about the other fields.

      What $/ does is controls where the <> file input operator stops reading. Normally it stops at the end of each line (after the newline character), but with $/ set to "*/", it will stop reading there instead. So with one read you can throw away everything up to that point, let your localized change to $/ fall out of scope at the closing brace so that the behavior of <> is back to normal, and then read the remainder of the field after the end of the comment. You'll miss fields 1-4 as well, since they were already skipped, but you can pick up the 'more text to check' part if there is something you want to do with that. My code as written calls the <> operator once more in void context to throw that and the following newline away, but you could instead assign that to a variable and do something with it.

      However, if you need to save fields 1-4 from the line where the comment ends, then you need to go with the other solution, i.e., keep track of whether you're in a comment or not and act accordingly. In that case if you are in a comment and detect */ in field five you could do two things: clear the comment flag, and remove the part up to the */ from the field. Similarly, if you are not in a comment but detect /* in field 5, you could remove the part starting with /* from the field and either set the comment flag right away (if you don't want to process that line at all) or else set a different flag that causes code at the end of the loop to set the comment flag after the line is processed.

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        OK thanks for the reply. This has been an eye-opening experience!
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