If your version of perl isn't recent, single-line if statements may not work for you.

Well, if by recent you mean a version of Perl >= 1.0. Quoting from perl.man.1 from the 1.0 source:

       Simple statements

...

      Any  simple  statement may optionally be followed by a single 
      modifier, just before the terminating semicolon.  The possible 
      modifiers are:

            if EXPR
            unless EXPR
            while EXPR
            until EXPR
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