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Re^3: substituted text is being interpreted

by dakkar (Hermit)
on Jan 06, 2005 at 16:13 UTC ( #419972=note: print w/ replies, xml ) Need Help??


in reply to Re^2: substituted text is being interpreted
in thread substituted text is being interpreted

It's a bit subtler than that.

When you write string literals, single-quoting them make them contain exactly the characters you typed, while double-quoting them activates the interpolation mechanism.

On the other hand, when you use a string as a regular expression, it gets interpreted by the regex engine.

For example:

$literal='abc@array$'; @array=(1,2,3); $interpolated="abc@array\$"; print 'literal: ',$literal,"\n"; print 'interp.: ',$interpolated,"\n"; if ($literal =~ /$literal/) { print "literal matches itself\n" } else { print "literal doesn't match itself\n" } $literal2='abc@array'; if ($literal2 =~ /$literal2/) { print "literal2 matches itself\n" } else { print "literal2 doesn't match itself\n" } if ($literal2 =~ /$literal/) { print "literal2 matches literal\n" } else { print "literal2 doesn't match literal\n" }

This prints:

literal: abc@array$ interp.: abc1 2 3$ literal doesn't match itself literal2 matches itself literal2 matches literal

The first two lines are hopefully obvious. As for the others:

  • $literal does not match itself because, seen as a regexp, it requires the string it matches to end with a y (the $ is interpreted by the regexp engine)
  • $literal2 does match itself. This is to confirm that the regexp is not "double-quote-interpolated-expanded-whathaveyou": the @ is still a single character.
  • $literal2 matches $literal because it does end in a y.
OK, for the pedants: the string between the // is interpolated, but its contents are not further expanded. I felt that this was more noise than signal, in this case.
-- 
        dakkar - Mobilis in mobile

Most of my code is tested...

Perl is strongly typed, it just has very few types (Dan)


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