use Perl

• Single quoted variable (Score:2)

  by Matts (1087) on 2006.07.31 7:52 (#49090) Journal

  Surely:
  
  is "$french_for{'$num'}", 'un', 'single quoted variable key';
  
  Will fail. You've single quoted '$num' hence you're looking for the key "\$num".

  Reply to This

  • Re:Single quoted variable (Score:2)

    by Ovid (2709)

    Yes, that's the failure, but I don't know why that should be obvious because if you add diag "'$num'" to the end of that script, you get this:

    # 'one'

    In other words, a variable in single quotes will interpolate if it's embedded in a double quoted string but not used as the key to a hash or an index into an array. That seems a bit odd and it would be nice if it were documented better. I should submit a patch for perltrap if it's not documented.
    • Re:Single quoted variable (Score:2)

      by Matts (1087)

      I tend to consider hash interpolation as being outside of the string, even though it's embedded. I consider there to be an invisible ". and ." around it.
    • Re:Single quoted variable (Score:1)

      by Smylers (2592)

      a variable in single quotes will interpolate if it's embedded in a double quoted string but not used as the key to a hash or an index into an array. That seems a bit odd

      Actually what seemed odd to me was that the first example (with single quotes around the literal) worked OK. But given that, I did expect it to fail round a variable (as in I guessed what the failure would be before even seeing your list of choices).

      Yes directly in a double-quoted string literal single quotes don't prevent a variable be
      • Re:Single quoted variable (Score:2)

        by Ovid (2709)

        Well, basically the stuff after a $ or @ sigil gets treated sort of like it's code to be executed. This leads to the following:

          temp $ touch foo.bar
          temp $ ls
          foo.bar
          temp $ perl -e 'print "$ENV{`rm foo.bar`}"'
          temp $ ls
          temp $

        I know you and I have discussed this bit, but others might want to be aware of it.