The mysterious monk's advice is incomplete. Trying this approach from the command line shows the problem:
#!perl
for $invalue (qw/ 1 -10 abc /) {
eval{ local $^W = 1; $invalue + 0 }; ### Is Number?
if ( $@ ) {
print "$invalue is *not* a Number; Details: $@\n";
} else {
print = "$invalue appears to be a number.\n";
}
}
produces:
1 appears to be a number.
-10 appears to be a number.
Argument "abc" isn't numeric in add at num.pl line 3.
abc appears to be a number.
The reason for this is that eval only traps errors, not warnings. The warning is printed directly to STDERR and $@ remains empty.
To fix this, you need to force the warning into an error. (And add an empty list assignment to silence the void context warning.):
#!perl
for $invalue (qw/ 1 -10 abc /) {
eval{ local $SIG{__WARN__} = sub { die @_ };
local $^W = 1; () = $invalue + 0 }; ### Is Number?
if ( $@ ) {
print "$invalue is *not* a Number; Details: $@\n";
} else {
print "$invalue appears to be a number.\n";
}
}
produces:
1 appears to be a number.
-10 appears to be a number.
abc is *not* a Number; Details: Argument "abc" isn't numeric in add at
+ num.pl line 4.
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