More operators in perl

x         The repetition operator. Returns a string consisting of the left operand repeated the number of times specified by the right operand. In an array context, if the left operand is a list in parens, it repeats the list.

print '-' x 80; # print row of dashes
print '-' x80; # illegal, x80 is identifier
print "\t" x ($tab/8), ' ' x ($tab%8); # tab over
@ones = (1) x 80; # an array of 80 1's
@ones = (5) x @ones; # set all elements to 5

x=        The repetition assignment operator. Only works on scalars.

..          The range operator, which is really two different operators depending on the context. In an array context, returns an array of values counting (by ones) from the left value to the right value. This is useful for writing "for (1..10)" loops and for doing slice operations on arrays.

In a scalar context, .. returns a boolean value. The operator is bistable, like a flip-flop, and emulates the line-range (comma) operator of sed, awk, and various editors. Each .. operator maintains its own boolean state. It is false as long as its left operand is false. Once the left operand is true, the range operator stays true until the right operand is true, AFTER which the range operator becomes false again. (It doesn't become false till the next time the range operator is evaluated. It can test the right operand and become false on the same evaluation it became true (as in awk), but it still returns true once. If you don't want it to test the right operand till the next evaluation (as in sed), use three dots (...) instead of two.) The right operand is not evaluated while the operator is in the "false" state, and the left operand is not evaluated while the operator is in the "true" state. The precedence is a little lower than

and &&. The value returned is either the null string for false, or a sequence number (beginning with 1) for true. The sequence number is reset for each range encountered. The final sequence number in a range has the string 'E0' appended to it, which doesn't affect its numeric value, but gives you something to search for if you want to exclude the endpoint. You can exclude the beginning point by waiting for the sequence number to be greater than 1. If either operand of scalar .. is static, that operand is implicitly compared to the $. variable, the current line number.



Examples:



As a scalar operator:

if (101 .. 200) { print; } # print 2nd hundred lines



next line if (1 .. /^$/); # skip header lines



s/^/> / if (/^$/ .. eof()); # quote body



As an array operator:

for (101 .. 200) { print; } # print $_ 100 times



@foo = @foo[$[ .. $#foo]; # an expensive no-op

@foo = @foo[$#foo-4 .. $#foo]; # slice last 5 items