Looks like in tr function a scalar variable is accepted as the fist argument, but is not compiled properly into set of characters 
$str1='abcde';
$str2='eda';
print "Test 1: strait set\n";
$diff1=$str1=~tr/$str2//;
$diff2=$str1=~tr/eda//;
print "   diff1=$diff1, diff2=$diff2\n";
print "Test 2: complement set\n";
$diff1=$str1=~tr/$str2//c;
$diff2=$str1=~tr/eda//c;
print "   diff1=$diff1, diff2=$diff2\n";

[download]
This produces in perl 5, version 26: 
Test 1: strait set
   diff1=0, diff2=3
Test 2: complement set
   diff1=5, diff2=2

[download]

Obviously only the second result in both tests is correct.

Looks like only explicitly given first set is correctly compiled.

Is this a feature or a bug ?

In reply to Strange behaviour of tr function in case the set1 is supplied by a variable by likbez

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