Programming Perl, 4th Edition

Ruby Traps

Matz, the creator of Ruby, stole heavily from Perl (and we think he chose a pretty good starting point). Actually, he put a Perl and a Smalltalk in a room and let them breed.

• There’s no irb. See the Python section.

• Perl just has numbers. It doesn’t care whether they have fractional portions or not.

• You don’t need to surround variables with {} (#{} in Ruby) to interpolate them, unless you need to disambiguate the identifier from the string around it:

  "My favorite language is $lang"

• Perl interpolated strings don’t have to be double-quoted: they can use qq with arbitrary delimiters. Similarly, generic uninterpolated strings don’t have to use single quotes: they can use a q with arbitrary delimiters.

  q/That's all, folks/
  q(No interpolation for $100)
  qq(Interpolation for $animal)

• You need to separate all Perl statements with a ;, even if they are on different lines. The final statement in a block doesn’t need a final ;.

• The case of variable names in Perl don’t mean anything to perl.

• The sigils don’t denote variable scope, nor even type. A $ in Perl is a single item, like $scalar, $array[0], or $hash{$key}.

• Perl compares strings with lt, le, eq, ne, ge, and gt.

• No magic blocks, but see PerlX::MethodCallWithBlock.

• Perl’s subroutine definitions are compile-phase. So:

  use v5.10;
  sub foo { say "Camelia" }
  foo();
  sub foo { say "Amelia" };
  foo();

  This prints Amelia twice, because the last definition is in place before the run-phase statements execute. This also means that the call to a subroutine ...