Programming Perl, 4th Edition

C Traps

Cerebral C programmers should take note of the following:

• Curlies are required for if and while blocks.

• You must use elsif rather than “else if” or “elif”. Syntax like this:

  if (expression) {
      block;
  }
  else if (another_expression) {      # WRONG
      another_block;
  }

  is illegal. The else part is always a block, and a naked if is not a block. You mustn’t expect Perl to be exactly the same as C. What you want instead is:

  if (expression) {
      block;
  }
  elsif (another_expression) {
      another_block;
  }

  Note also that “elif” is “file” spelled backward. Only Algol-ers would want a keyword that was the same as another word spelled backward.

• The break and continue keywords from C become in Perl last and next, respectively. Unlike in C, these do not work within a do {} while construct.

• For a long time Perl had no equivalent to C’s switch statement. Perl v5.10 introduced a “switch on steroids” with the fancy name given–when (since it’s a fancier construct). See Chapter 4. It’s easy to build your own, too; see and in Chapter 4.

• Variables begin with $, @, or % in Perl.

• Comments begin with #, not /*. Use pod for multiline comments.

• You can’t take the address of anything, although a similar operator in Perl is the backslash, which creates a reference. You get something that looks like an address when you stringify a reference, but you can’t really use it for anything.

• ARGV must be capitalized. $ARGV[0] is C’s argv[1], and C’s argv[0] ends up in $0. See Chapter 25.

• Syscalls such as link, unlink, and rename return true ...