After reading the resources that you all posted, and re-reading my chapter, I have mangaed to narrow my question. Obviously, the way that I am reading this code is incorrect because I don't think that it should work but when I tested it I found that it did. Please tell me where my error in thinking is. It comes straight from my perl book. It is supposed to parse a string in order to determine if the string contains aeiou in order.
#!/usr/bin/perl -w
while (<>) {
print if
(/^[^aeiou]*a[^eiou]*e[^aiou]*i[^aeou]*o[^aeiu]*u[^aeio]*$/);
}
It is my understanding that the code should match if and only if there is a non vowel character at the beginning of the string, an a followed by any number of characters except for other vowels, an e followed by any number of characters except for any number of vowels etc... and finally a u followed by any number of characters that are not other vowels at the end of the string.
My questions:
-The ^ anchor before the first set of brackets seems to me to say that the string must begin with a non vowel character in order to match. I tested this theory and as long as the vowels are in order the string can begin with a non vowel character. How does that work?
-Why does the if statement not require brackets?
-Why is the $ anchor necessary at the end? Wouldn't the regular expression do the same thing if it were left off?
Thanks!!! | [reply]
[d/l] |
there is a non vowel character at the beginning of the string
No, and this is the misunderstanding. * means zero or more, so there can also be no non-vowel character at the beginning (and anywhere in between, either).
| [reply] |
It is my understanding that the code should match if and only if there is a non vowel character at the beginning of the string...
No, see Quantifiers in perlre, and contrast * with + (see choroba’s answer above).
Why does the if statement not require brackets?
See Statement Modifiers in perlsyn.
Why is the $ anchor necessary at the end?
In this particular case, it probably isn’t. Update: See the answer by MidLifeXis below.
HTH,
Athanasius <°(((>< contra mundum
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The pattern also has one other restriction - that there are exactly five vowels, plus other characters in between. Without the final set of non-vowel matches and the end of string character, this restriction would not be enforced.
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