Help:Why does eval add a 1 behind evaluations?

[Tay Ray Chuan]

Hi, I tried using eval like this:

print "Enter something to evaluate:\n";
while (defined($s = <>)) {
$result = eval $s;
if ($@) {
print "Invalid string:\n $s";
} else {
print "$result\n";
}
}

this can evaluate anything. but when I type this:

"$a=5;$b=5;$c=$a+$b;print $c;", it prints "101".

Why is there an extra "1"?

 

[Tore Aursand]

print "Enter something to evaluate:\n";
while (defined($s = <>)) {
$result = eval $s;
if ($@) {
print "Invalid string:\n $s";
} else {
print "$result\n";
}
}

this can evaluate anything. but when I type this:
"$a=5;$b=5;$c=$a+$b;print $c;", it prints "101".

Why is there an extra "1"?

You really should have read 'perldoc -f eval';

"[...] In both forms, the value returned is the value of the
last expression evaluated inside the mini-program [...]"

In other words: 'print $c;' returns 1.

 

[Joe Smith]

Hi, I tried using eval like this:

print "Enter something to evaluate:\n";
while (defined($s = <>)) {
$result = eval $s;
if ($@) {
print "Invalid string:\n $s";
} else {
print "$result\n";
}
}

this can evaluate anything. but when I type this:

"$a=5;$b=5;$c=$a+$b;print $c;", it prints "101".

Why is there an extra "1"?

Change
print "$result\n";
to
print "The result from eval() is $result\n";
and it will show what is really happening.
-Joe

 

[Tad McClellan]

Hi, I tried using eval like this:

print "Enter something to evaluate:\n";
while (defined($s = <>)) {
$result = eval $s;
if ($@) {
print "Invalid string:\n $s";
} else {
print "$result\n";
}
}

this can evaluate anything. but when I type this:

"$a=5;$b=5;$c=$a+$b;print $c;", it prints "101".

Why is there an extra "1"?

The last expression eval()uated is the value of the eval(), so
$result gets print()'s return value (1).

So, the

print $c

outputs the 10

then

print "$result\n";

outputs the 1 and a newline.