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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"?

Tay Ray Chuan wrote:
> 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.


--
Tore Aursand <>

In article < >,
Tay Ray Chuan <> wrote:
>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

--
See http://www.inwap.com/ for PDP-10 and "ReBoot" pages.

Tay Ray Chuan <> wrote:
> 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.



--
Tad McClellan SGML consulting
Perl programming
Fort Worth, Texas