in reply to Re^2: In place search and replace with a hash
in thread In place search and replace with a hash

c:\@Work\Perl\monks>perl -wMstrict -le
"my %hash = ('$1' => 'oops',  'abc' => 'ok');
 ;;
 'abc' =~ m{ (abc) }xms;
 print qq{captured '$1'};
 ;;
 print $hash{'$1'};
"
captured 'abc'
oops

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Re^4: In place search and replace with a hash
by LanX (Saint) on Dec 28, 2014 at 02:59 UTC
    You missed the point. Imho RHS of s/// isn't evaluated w/o e flag.

    Cheers Rolf

    (addicted to the Perl Programming Language and ☆☆☆☆ :)

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        > ?

        Well AnoMonk said "single quotes ... prevent variable interpolation" that's misleading.

        update

        maybe clearer with an example

          DB<106> %h = (x => 0, '$1' => 1);
 => ("x", 0, "\$1", 1)

  DB<107> $s = 'axb'
 => "axb"

  DB<108> $s =~ s/(x)/'$1'/r;             # no prevention
 => "a'x'b"

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        single quotes on the RHS of s/// never prevent interpolation.

        Interpolation is the process to translate "$a $h{$b}" to $a . " " . $h{$b} at compile time.

        But the keys of a hash-fetch are not interpolated they are executed, otherwise something like $h{$a$b} wouldn't cause a syntax error.

        Cheers Rolf

        (addicted to the Perl Programming Language and ☆☆☆☆ :)

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Re^4: In place search and replace with a hash
by hkates (Novice) on Dec 28, 2014 at 03:11 UTC
    Hi AnomalousMonk, thanks for your reply. I probably should have specified that I'm pretty new to perl. Could you comment at all at what your code does?
[reply]

      The code example above was meant as a counter-example to what I understood LanX to be saying. Comments: 

      my %hash = ('$1' => 'oops',  'abc' => 'ok');  # create a hash

'abc' =~ m{ (abc) }xms;   # capture a sub-string to $1
print qq{captured '$1'};  # show what that string is

print $hash{'$1'};  # show effect of single-quotes: no interpolation

      [download]
      Had  $1 been used directly (as in $hash{ $1 }), the output would have been 'ok'. A more complete example: 
      c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my %hash = ('$1' => 'oops',  'abc' => 'ok');
 dd \%hash;
 ;;
 'abc' =~ m{ (abc) }xms;
 print qq{captured '$1'};
 ;;
 print 'single-quoted: ', $hash{'$1'};
 print 'straight: ', $hash{ $1 };
"
{ "\$1" => "oops", "abc" => "ok" }

captured 'abc'
single-quoted: oops
straight: ok

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