You don't check whether the eval succeeds or not. In fact, it is failing, as you can see by printing $@: 
my $op = shift;
for (qw/your hand is too cold to hold/) {
   eval $op;
   print $@, $_, $/;
}

__OUTPUT__

Modification of a read-only value attempted at (eval 1) line 1.
your
Modification of a read-only value attempted at (eval 2) line 1.
hand
Modification of a read-only value attempted at (eval 3) line 1.
is
Modification of a read-only value attempted at (eval 4) line 1.
too
Modification of a read-only value attempted at (eval 5) line 1.
cold
Modification of a read-only value attempted at (eval 6) line 1.
to
Modification of a read-only value attempted at (eval 7) line 1.
hold

[download]
One way to fix it is to change the for loop to for my $x (...) and add local $_ = $x at the top of the loop.

blokhead

In reply to Re: Using eval to s/// with a pattern supplied on the command-line by blokhead
in thread Using eval to s/// with a pattern supplied on the command-line by ChrisS

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