What do you find odd?. With alternation | Perl will match the first element if it can, if not the next ... so in the first case it finds a 1 which satisfies the first capture and then the second capture takes the optional 2. In the second case you get 12 as the first capture and then the second captuere 2? 'matches' the 3 as 3 is 0 or more 2s..... (actually it matches the null string between 2 and 3 to be technically correct.
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Does this mean that leftmost-longest rule is not true for perl?
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Out of perldoc perlre:
Alternatives are tried from left to right, so the first alternative
found for which the entire expression matches, is the one that is
chosen. This means that alternatives are not necessarily greedy. For
example: when matching "foo|foot" against "barefoot", only the "foo"
part will match, as that is the first alternative tried, and it
successfully matches the target string. (This might not seem important,
but it is important when you are capturing matched text using
parentheses.)
Let's look at a simply modified test sample:
/(1|12)(3?)/
will match 1 because 3 ist optional
and
/(1|12)(3?)$/ # use anchor to force the engine to match the entire ex
+pression
will match 12 because it has to satisfy the entire expression and so it will match 3 at the end of the string
Add:
For clarifying, the first example will have '1' in $1 and nothing in $2
Second example will have '12' in $1 and '3' in $2
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Greedy matching applies to the closures, not to alternatives. Besides, in this case, whether 12 matches or 1 then 2, it's the same length, is it not? From perlre, "alternatives are not necessarily greedy." You can make your matches greedy by arranging them how you like.
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$_ = '123';
if(/(1|12)(2?)/)
{
print "1=[$1] 2=[$2]\n";
}
if(/(12|1)(2?)/)
{
print "1=[$1] 2=[$2]\n";
}
and compare (left to right).
MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!" | I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README). | ** The third rule of perl club is a statement of fact: pod is sexy. |
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