Question

there:
I’m new to Perl, and get a string concatenation problem of it. I have two strings below:

my $string1 = "hello\U\Q \t\n\f\b\aWorld" . "\n" . "\E";
my $string2 = "hello\U\Q \t\n\f\b\aWorld\n\E";

They are looked the same to me, until i print them out.
$string1 looks like this:

hello\ \    \
\
 \WORLD

and with a bell ring.

$string2 is this one:

hello\ \    \
\
 \WORLD\

with the same bell ring, and a backslash at the tail.

Why does $string2 get a backslash at its end but $string1 doesn’t?

Answer 1

When you use \Q you’re telling it to quote (put a backslash in front of) all the characters that aren’t matched by \w. The result is that you’re getting a backslash added every time there’s a backslash in your code. e.g. \a creates the bell sound but your string gets a backslash added in. When you use \Q it behaves this way until you reach \E or get to the end of the string.

When you create $string1 you actually have 3 separate strings that you’re adding together so they’re evaluated separately. The result is that only the first of the 3 is affected by the \Q.

In the second example the \n\E results in \\ in the string. When you print this out it results in the trailing backslash you’re seeing.

Hope that makes sense.