You would use ... in the case where you could have the begin and end condition on the same line, but don't want that to be considered as having met the end condition.
my $save = tell( DATA );
while( <DATA> ) {
print if /a/ .. /z/;
}
print "-" x 5, "\n";
seek( DATA, $save, 0 );
while( <DATA> ) {
print if /a/ ... /z/;
}
exit 0
__DATA__
a b z
c d
w q
z
| [reply]
[d/l] |
'..' -- the range operator
'...' -- the range operator, but: "The operator ... doesn't return true if both its tests are true on the same line, .. does.
(Perl Coookbook -- 6.8 Extracting a Range of Lines)
----
I Go Back to Sleep, Now.
OGB
| [reply] |
What's going on here? Shouldn't '...' be a syntax error?
Nope. See perlop:
If you don't want it to test the right operand till the next
evaluation, as in sed, just use three dots ("...") instead of two. In
all other regards, "..." behaves just like ".." does.
| [reply] |
In scalar context, perl treats the .. and ... operators as only slightly different from one another, just like the other repondants said. Thus:
if(a() ... b()) { # etc
and
if(a() .. b()) { # etc
are almost, but not exactly the same. That's the reason why both exist.
In list context, that is, the way you were using it, they appear to act exactly the same. I can't, in the same perspective, really imagine
print 3 .. 3;
to behave differently from
print 3 ... 3;
Can you?
| [reply]
[d/l]
[select] |
Well, it does seem a little odd to me to have
echo -e "1\n2\n3\n4" | perl -lne 'print if 2..2'
return the same as
perl -le 'print 2..2'
while
echo -e "1\n2\n3\n4" | perl -lne 'print if 2...2'
returns something very different from
perl -le 'print 2...2'
I understand why it does, but it would seem preferable to either disallow ... in list context, or make it behave "the same" in list and scalar contexts. (So the list 2...2 would be 2,3,...,INTMAX, and the list a()...b() would be the same as a()..b() unless a()==b(), in which case it would be a(),...,INTMAX.)
Although, come to think of it, I think what would really make sense is if someone wrote a source filter than numbers all of the operators, with .. in slot 2 and ... in slot 3, so that you can use a sequence of periods of the appropriate length to choose any operator in Perl. Perl likes gathering up different programming paradigms, right? (Functional, OO, logical, ...) So this would make it easier to implement the genetic algorithm style, where you start off with something simple like
$x = $x ....... $y ...... $z ...... $x;
$y = $x ...... $y ........... $z;
$z = $x .... $y ........ $z;
and then you can easily mutate and interbreed code merely by changing the number of periods. Repeat until you get the answer desired. Some of my debugging sessions already closely resemble this. | [reply]
[d/l]
[select] |
The "..." is in Perl 5 only to make the sed-to-perl translator more accurate. It's not expected the most people would use it. Note also that either kind of scalar range operator is going away in Perl 6 in favor of a flipflop() function or some such. "$a..$b" will always produce a range list,
and "$a..." will mean the same as "$a..Inf" (meaning you shouldn't use it where it will get flattened, unless you have a lot of memory...) | [reply]
[d/l]
[select] |
| [reply] |