in reply to Assigning the result of a chomp to the chomped var itself.

I have a behavior that is even more difficult to understand (running Perl 5.14.4).

Running the test directly under the Perl debugger: 

  DB<1> $x = "a\n";

  DB<2> $x = chomp $x;

  DB<3> print $x
1

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And running the same at the command line: 
$ perl -E 'my $x = "a\n";  $x = chomp $x; say $x'
0

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So I get 1 under the debugger et 0 at the command line. Isn't it strange?

And, BTW, using another variable solves the issue: 

$  perl -E 'my $x = "a\n"; my $y = chomp $x; say $y;'
1

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This leads me to believe that doing this: 
$x = chomp $x;

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might well be undefined behavior (and should most probably be avoided), just as: 
$c = ++$c;

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is undefined both in C and in Perl. (And different C compilers actually give different results on the code above, I have tried it once in the past.)

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Re^2: Assigning the result of a chomp to the chomped var itself.
by Anonymous Monk on Nov 26, 2014 at 20:02 UTC

    Interesting...

    $ perl -wMstrict -e 'my $x = "a\n";  $x = chomp $x; print "<$x>\n"'
<0>
$ perl -wMstrict -e 'our $x = "a\n";  $x = chomp $x; print "<$x>\n"'
<1>
$ perl -wMstrict -MO=Terse -e 'our $x; $x = chomp $x;'
LISTOP (0x8aa33b8) leave [1] 
    OP (0x8aa3694) enter 
    COP (0x8aa33dc) nextstate 
    UNOP (0x8aa3414) null [15] 
        SVOP (0x8aa3434) gvsv  GV (0x8a9e5c0) *x 
    COP (0x8aa36b8) nextstate 
    BINOP (0x8aa36f0) sassign 
        UNOP (0x8aa3714) schomp [2] 
            UNOP (0x8aa3750) null [149] 
                UNOP (0x8aa3774) null [15] 
                    SVOP (0x8aa3794) gvsv  GV (0x8a9e5c0) *x 
        UNOP (0x8aa3368) null [15] 
            SVOP (0x8aa3398) gvsv  GV (0x8a9e5c0) *x 
$ perl -wMstrict -MO=Terse -e 'my $x; $x = chomp $x;'
LISTOP (0x92913d8) leave [1] 
    OP (0x9291754) enter 
    COP (0x92913fc) nextstate 
    OP (0x9291434) padsv [1] 
    COP (0x929171c) nextstate 
    UNOP (0x9291778) schomp [1] 
        UNOP (0x9291368) null [149] 
            OP (0x92913a0) padsv [1]

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