Perl: Double Quotish Evaluation
| This first example makes a good solution that works in all cases. | |
| Perl Script | Output |
|---|---|
my( $a, $b, $c ) = qw/aaa bbb ccc/; my $rog = '>>> $a "$b"} $c <<<'; printf("%s\n%s\n", $rog, &dqn( $rog ) ); sub dqn{ ($_ = shift) =~ s/"/\\"/g; eval(qq{"$_"}); } |
>>> $a "$b"} $c <<< >>> aaa "bbb"} ccc <<< |
| Here, all is well with this test case, but see the following example shows problems. | |
| Perl Script | Output |
my( $a, $b, $c ) = qw/aaa bbb ccc/; $rog = '>>> $a $b $c <<<'; print "$rog\n"; print eval '"' . $rog . '\n"'; print eval qq/"$rog\n"/; print eval qq{"$rog\n"}; print eval "qq{$rog\n}"; print eval "\\\"$rog\n\\\""; |
>>> $a $b $c <<< >>> aaa bbb ccc <<< >>> aaa bbb ccc <<< >>> aaa bbb ccc <<< >>> aaa bbb ccc <<< |
| If the string contains quotes, we get problems with all but one. The last one can also fail. See the next example. | |
| Perl Script | Output |
my( $a, $b, $c ) = qw/aaa bbb ccc/; $rog = '>>> $a "$b" $c <<<'; print "$rog\n"; print eval "qq{$rog\n}"; # These all fail. # print eval '"' . $rog . '\n"'; # print eval qq/"$rog\n"/; # print eval qq{"$rog\n"}; # print eval "\\\"$rog\n\\\""; |
>>> $a "$b" $c <<< >>> aaa "bbb" ccc <<< |
| We had got aroung quote problems using {}, but if these are unbalanced, they also fail. Note: The 2nd example here ('Works ?') works or fails depending on the perl version. | |
| Perl Script | Output |
my( $a, $b, $c ) = qw/aaa bbb ccc/; $rog = '>>> $a "$b" $c <<<'; ##### Works ##### $rog = '>>> $a {"$b"} $c <<<'; print eval "qq{$rog\n}"; ##### Works ? ##### $rog = '>>> $a {"$b" $c <<<'; print eval "qq{$rog\n}"; ##### Breaks ##### $rog = '>>> $a "$b"} $c <<<'; print eval "qq{$rog\n}"; |
Scalar found where operator expected at
(eval 3) line 1, near "qq{>>> $a "$b"} $c"
>>> aaa {"bbb"} ccc <<<
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Roger Hall COMPUSPEC |
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